powerpc: Merge in the ppc64 version of the prom code.
This brings in the ppc64 version of prom_init.c, prom.c and btext.c and makes them work for ppc32. This also brings in the new calling convention, where the first entry to the kernel (with r5 != 0) goes to the prom_init code, which then restarts from the beginning (with r5 == 0) after it has done its stuff. For now this also brings in the ppc32 version of setup.c. It also merges lmb.h. Signed-off-by: Paul Mackerras <firstname.lastname@example.org>