Add armv7l support for grub2

We have at least one armv7l EFI machine that runs EFI grub2. Enable
the grub2 installation code to handle the translation from "armv7l" (uname)
to "arm" (grub2 name)

Signed-off-by: Alexander Graf <agraf@suse.de>
Merge pull request #53 from agraf/master

Add armv7l support for grub2