[Linaro-uefi] The GRUB multiboot support patch for aarch64(V2)

Hi Leif, I have make a new multiboot support patch following your suggestion: (1)break the multiboot-spcecific code out into a separate source file: multiboot.c (2)use more generic terminology (3)try to avoid change existing Linux loader

I have tested it locally, it works fine for me.

Please check the patch, and provide some suggestions.

Thank you very much! :-)