Added EFI support for none aarch64 arm systems

There are armv7 based boards which comes with an EFI
firmware. In order to boot them we have to make sure
to use grub2 bootarm.efi and call the right grub2
bootloader configuration methods (bnc #908469)
Merge pull request #418 from openSUSE/review_141208_armv7_grub2_support

Added EFI support for none aarch64 arm systems