Let the grub2 package take care of creating installable grub2 images,
this will allow creating grub2 images without first calling x86 image
generation recipe. Also as side effect, since those images are now
shared, it'll reduce the number of calling grub-mkimage.
Signed-off-by: Tomasz Maciej Nowak <tomek_n@o2.pl>
[rebase, adjusted commit title]
Signed-off-by: Paul Spooren <mail@aparcar.org>
