Fix problems of the squashed update to 3.4.48 kernel version
by reverting "mm/pagewalk.c: walk_page_range should avoid VM_PFNMAP areas"

This reverts commit:
https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/?id=c8a097fd8d73584d7c1577e0aee41c2a177394f7

The changes made by this commit caused kernel panics while performing
memory operations with subsequent hangs, reboots or shutdowns.