Add grub2 for Power

Signed-off-by: Dinar Valeev <dvaleev@suse.com>
PowerPC kernel is vmlinux

Signed-off-by: Dinar Valeev <dvaleev@suse.com>
Don't write MBR ID on non x86 architectures

Signed-off-by: Dinar Valeev <dvaleev@suse.com>
Rewrite searchOFBoot function

Use chosen/bootpath from device-tree to find a device we've booted from.
This is more reliable than searching for PROM id, which is not available
under KVM

Signed-off-by: Dinar Valeev <dvaleev@suse.com>