Add PReP GPT support for POWER

This commit adds PReP GPT for POWER.

Signed-off-by: Dinar Valeev <dvaleev@suse.com>
Merge branch 'master' of https://github.com/openSUSE/libstorage

Conflicts:
	package/libstorage.changes
Merge pull request #57 from k0da/master

Add PReP GPT support for POWER