Improve mkuzip(8) and geom_uzip(4), merge in LZMA support from mkulzma(8)
and geom_uncompress(4):

1. mkuzip(8):
   • Proper support for eliminating all-zero blocks when compressing an image. This feature is already supported by the geom_uzip(4) module and CLOOP format in general, so it's just a matter of making mkuzip(8) match. It should be noted, however that this feature while it sounds great, results in very slight improvement in the overall compression ratio, since compressing default 16k all-zero block produces only 39 bytes compressed output block, which is 99.8% compression ratio. With typical average compression ratio of amd64 binaries and data being around 60-70% the difference between 99.8% and 100.0% is not that great further diluted by the ratio of number of zero blocks in the uncompressed image to the overall number of blocks being less than 0.5 (typically). However, this may be important from performance standpoint, so that kernel are not spinning its wheels decompressing those empty blocks every time this zero region is read. It could also be important when you create huge image mostly filled with zero blocks for testing purposes.
   • New feature allowing to de-duplicate output image. It turns out that if you twist CLOOP format a bit you can do that as well. And unlike zero-blocks elimination, this gives a noticeable improvement in the overall compression ratio, reducing output image by something like 3-4% on my test UFS2 3GB image consisting of full FreeBSD base system plus some of the packages (openjdk, apache etc), about 2.3GB worth of file data (800+MB compressed). The only caveat is that images created with this feature "on" would not work on older versions of FeeBSDxi kernel, hence it's turned off by default.
   • provide options to control both features and document them in manual page.
   • merge in all relevant LZMA compression support from the mkulzma(8), add new option to select between both.
   • switch license from ad-hoc beerware into standard 2-clause BSD.

2. geom_uzip(4):
   • implement support for de-duplicated images;
   • optimize some code paths to handle "all-zero" blocks without reading any compressed data;
   • beef up manual page to explain that geom_uzip(4) is not limited only to md(4) images. The compressed data can be written to the block device and accessed directly via magic of GEOM(4) and devfs(4), including to mount root fs from a compressed drive.
   • convert debug log code from being compiled in conditionally into being present all the time and provide two sysctls to turn it on or off. Due to intended use of the module, it can be used in environments where there may not be a luxury to put new kernel with debug code enabled. Having those options handy allows debug issues without as much problem by just having access to serial console or network shell access to a box/appliance. The resulting additional CPU cycles are just few int comparisons and branches, and those are minuscule when compared to data decompression which is the main feature of the module.
   • hopefully improve robustness and resiliency of the geom_uzip(4) by performing some of the data validation / range checking on the TOC entries and rejecting to attach to an image if those checks fail.
   • merge in all relevant LZMA decompression support from the geom_uncompress(4), enable automatically when appropriate format is indicated in the header.
   • move compilation work into its own worker thread so that it does not clog g_up. This allows multiple instances work in parallel utilizing smp cores.
   • document new knobs in the manual page.

Reviewed by: adrian
MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D5333