[BUG] grub-efi memeory map size is too small

[Mao, Bibo]

        In function kern/efi/mm.c, macro MEMORY_MAP_SIZE is defined as
0x1000, on some platform, its memory map size is larger than
MEMORY_MAP_SIZE. And there is another function find_mmap_size which is
defined in loader/i386/efi/linux.c , I do not know whether this function
can be put in file mm.c, and get memory_map_size by find_mmap_size
function.


Thanks
Bibo,mao