[1/5][POWERPC] boot: prepare for zImage.kexec

[Paul Mackerras]

Milton Miller writes:

> This patch moves the initializations of prom variables to boot/prom.c
> to allow it to be replaced for kexec.   Kexec does not care about
> the stdout handle, but will care about the location of the device
> tree and will search for RTAS.

Unfortunately it doesn't apply now because of other changes to
boot.h.  Please respin the series against the powerpc.git tree.

Thanks,
Paul.