[IA64] simplified efi memory map parsing

New version leaves the original memory map unmodified.
Also saves any granule trimmings for use by the uncached
memory allocator.

Inspired by Khalid Aziz (various traces of his patch still
remain).  Fixes to uncached_build_memmap() and sn2 testing
by Martin Hicks.

Signed-off-by: Tony Luck <tony.luck@intel.com>