grub-efi: change to generate EFI image in target package
To generate the target EFI image in a native package, it requires
the host gcc have the ability to do -m32/-m64 compiling, but gcc
doesn't have that support on the 32bit version of some distributions
(e.g. rehl, suse), it would fail when build a 64bit target on these
32bit hosts.
In fact, all we need from grub-efi-native is the grub-mkimage binary,
so change the solution to:
* grub-efi-native only install grub-mkimage
* grub-efi compiles target modules, generates EFI image
with grub-mkimage and deploy, but install nothing.
