Update the AP135 reference design flash layout to be more useful.

• Shuffle the kernel to be at the beginning
• Give the kernel 2mb, the rootfs 6mb, and 'mib0' the rest
• put the cfg parition just before the ART calibration data for the wifi part in the SoC
• .. and make sure ART points to the right 64k region.

I've updated the freebsd-wifi-build wiki the instructions on using this.

If someone has an AP135 with 8MB SPI flash then this won't work; everything
minus the big mib0 partition is just a bit over 8MB. Come see me if this
ever happens (you'll likely just have to shrink the rootfs and the kernel
a little in order to make it fit.)

Tested:

• AP135 reference board.