Add runtime option for all second-stage boot blocks to reset terminal

[lev]

Summary

Some hardware/firmware leaves serial console in bogus state before calling user boot code. After that output of boot2, gptboot and other second level boot blocks could not be seen by user, which is inconvenient.
This diff adds new runtime option -R, which force all these boot blocks to send default VT-100 reset command <ESC>c before all output. This sequence could be changed with build time option BOOT_COMCONSOLE_RESET_TERM_CMD.

[imp]

lots of duplication in this area still :( that's beyond this review.
except for the duplication you added: it can be done in defs.mk.
boot2 is always short of space, how are we doing?

stand/i386/boot2/boot2.c

419

So this adds about 30-40 bytes of code to boot2. We've had size issues with this code forever... how are we doing these days for size?

stand/i386/gptboot/Makefile

13

Put this in stand/def.mk. No need to repeat it everywehere.

stand/i386/isoboot/isoboot.c

61

It would be nice to abstract the 'small parsing routines' down into one copy rather than the 6 we have in the tree today.

[lev]

stand/i386/boot2/boot2.c

419

It works for me :-)

# pwd
/usr/obj/nanobsd/gateway.v3/data/src/amd64.amd64/stand/i386/boot2
# ls -la boot2*
-rw-r--r--  1 root  wheel   7680 Feb 24 21:28 boot2
-rwxr-xr-x  1 root  wheel   5352 Feb 24 21:28 boot2.bin
-rw-r--r--  1 root  wheel     23 Feb 24 21:28 boot2.h
-rw-r--r--  1 root  wheel   7576 Feb 24 21:28 boot2.ld
-rw-r--r--  1 root  wheel    512 Feb 24 21:28 boot2.ldr
-rw-r--r--  1 root  wheel  10296 Feb 24 21:28 boot2.o
-rwxr-xr-x  1 root  wheel  15300 Feb 24 21:28 boot2.out
#

stand/i386/isoboot/isoboot.c

61

I'm not sure, that it should be done in this change.

[freqlabs]

sbin/reboot/boot_i386.8

236

reset the serial terminal
the serial terminal in an unspecified or bogus state. The reset sequence

stand/i386/gptzfsboot/Makefile

13

This doesn't seem right.

stand/i386/zfsboot/zfsboot.c

699–700

The white space in this block breaks the convention of the rest of this file.

[freqlabs]

Whoops, spotted a few more spelling errors.

sbin/reboot/boot_i386.8

235

s/prevous/previous/

237

s/overriden/overridden/

[freqlabs]

sbin/reboot/boot_i386.8

108

Should add R preceding r here.

169

Should add R preceding r here as well.

[lev]

Rebase & fix conflicts

[lev]

Regenerate against new git repository