Experimental ABLE firmware support

Hi,

Just a quick email to let people know that -current now has support for
ABLE firmware.  Both running a.out and ELF kernels.

Note that currently there are issues with ABLE that I'm working with
simtec to resolve.  These include:
Not booting from ffs
bootargs not being passed in
Note my testing hasn't been that thorough, I can boot kernels from
tftpboot via my tulip/de card, but you have to enter by hand the root
device, etc.  So I'd not recommend ABLE for those who need a system that
just boots.

Something I'm still looking into is how to handle symbol support on ELF
kernels.  Not sure if we need to do the SYMTAB_SPACE trick still.

Cheers,
Chris