ANDROID: arm64: mm: fix 4.4.154 merge

android-4.4 contains an out-of-tree backport of 68709f45385a ("arm64:
only consider memblocks with NOMAP cleared for linear mapping"), so it
should use the 4.9.y implementation of pfn_valid() that calls
memblock_is_map_memory().

Change-Id: Id1d67813ee2a0a85ec69ef255daa27c4f6286800
Reported-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Greg Hackmann <ghackmann@google.com>