This fixes a problem in EFI memory map trimming. For example,
here's part of the memory map on my i2000:

    mem00: type=4, attr=0x9, range=[0x0000000000000000-0x0000000000001000) (0MB)
    mem01: type=7, attr=0x9, range=[0x0000000000001000-0x0000000000088000) (0MB)
    mem02: type=4, attr=0x9, range=[0x0000000000088000-0x00000000000a0000) (0MB)
    mem03: type=5, attr=0x8000000000000009, range=[0x00000000000c0000-0x0000000000100000) (0MB)
    mem04: type=7, attr=0x9, range=[0x0000000000100000-0x0000000004000000) (63MB)
    mem05: type=2, attr=0x9, range=[0x0000000004000000-0x00000000049ba000) (9MB)
    mem06: type=7, attr=0x9, range=[0x00000000049ba000-0x000000007ec0b000) (1954MB)
    ...

There's a hole at 0xa0000-0xc0000, so we should ignore all the WB memory
in that granule.  With 16MB granules, the existing code trims like this
(note the 4K page at 0x0 should have been ignored, but wasn't).