Restructures early code path on ieee1275 to unify grub_main() as
the first C function that is executed in every platform.
* include/grub/ieee1275/ieee1275.h (grub_ieee1275_init): New prototype.
* kern/i386/ieee1275/startup.S (_start): Jump to grub_main() instead of
cmain().
* kern/powerpc/ieee1275/crt0.S (_start): Likewise.
* kern/ieee1275/cmain.c (cmain): Rename to ...
* kern/ieee1275/cmain.c (grub_ieee1275_init): ... this.
* kern/ieee1275/init.c (grub_machine_init): Call grub_ieee1275_init()
at the beginning.