GRUB_IEEE1275_FLAG_NO_PRE1_5M_CLAIM.
* kern/ieee1275/cmain.c (grub_ieee1275_find_options): Set
GRUB_IEEE1275_FLAG_NO_PRE1_5M_CLAIM on qemu.
* kern/ieee1275/init.c (grub_claim_heap): Don0t allocate below
1.5MiB if GRUB_IEEE1275_FLAG_NO_PRE1_5M_CLAIM is set.