Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFp4:
Add support for the CENTIPAD board (http://www.harerod.de/centipad/index.html)
(which is a very cool, very small ARM board)
Add support for KB9202B (it has different memory)
Make BOOT_FLAVOR settable
Minor cleanup nits

Approved by: re@

MFp4: boot on KB9202 correctly. Also, reduce the size of the SD/MMC driver
somewhat.

MFp4:

Massive update. The highlights:
o dramatically cut memory usage by writing better, less intertwingled
code.
o implement booting off mmc/sd cards (sd only tested one at the moment)
o start to split out board specific stuff for boot2.

MFp4: First cut at making spi and/or sd card booting work, needs work

MFp4: Numerous changes from p4 to try to improve tftp downloading,
reduce code footprint, etc. While some problems still remain, the
reliability of tftp is much improved.

MFp4 (checkpoint of work in progress):

o Use a directory layout that is more akin to the i386 boot layout.
o Create a libat91 for library routines that are used by one or more
of the boot loaders.
o Create bootiic for booting from an iic part.
o Create bootspi for booting from an spi part.
o Optimize the size of many of these routines (especially emac.c). Except
for the emac.c optimizations, all these have been tested.
o eliminate the inc directory, libat91 superceeds it.
o Move linker.cfg up a layer to allow it to be shared.