DESC
remap_file_pages protection support: support private vma for MAP_POPULATE
EDESC
From: Ingo Molnar <mingo@elte.hu>

If we're not rearranging pages, support even PRIVATE vma.

This is needed to make MAP_POPULATE|MAP_PRIVATE to work, since it calls
remap_file_pages.

Notes from: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>

We don't support private VMA because when they're swapped out we need to store
the swap entry in the PTE, not the file offset and protections; so, I suppose
that with remap-file-pages-prot, we must punt on private VMA even when we're
just changing protections. This change is in a separate patch.
