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

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

Strip out the useless junk. All we really care about is the text,
data and bss sections. All the rest is needed for normal binaries,
but boot loaders aren't normal.

No need to list an obsolete arm compiler here.

Don't need __DYNAMIC here. it is commented out and a.out only -- these are all ELF.

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.