kvm: powerpc: allow guest control "G" attribute in mas2

"G" bit in MAS2 indicates whether the page is Guarded.
There is no reason to stop guest setting  "G", so allow him.

Signed-off-by: Bharat Bhushan <bharat.bhushan@freescale.com>
Signed-off-by: Alexander Graf <agraf@suse.de>