What we unmap there are mappings we better wouldn't have established in
the first place. Arrange for us to only ever map RAM, and then drop the
unmapping code, which was flawed anyway.

Nothing with a similar effect as patch 1 needs doing for xen.efi: Prior
to GNU binutils commit a844415db878 ("bfd/PE: correct SizeOfImage
calculation") too large a size was calculated. With that change in place,
image size is properly rounded up to a multiple of 2Mb.

1: mkelf32: pad load segment to 2Mb boundary
2: mm: drop unmapping from marking-as-I/O in arch_init_memory()

Jan