HWPOISON: Add invalidate_inode_page

Add a simple way to invalidate a single page
This is just a refactoring of the truncate.c code.
Originally from Fengguang, modified by Andi Kleen.

Signed-off-by: Andi Kleen <ak@linux.intel.com>

diff --cc include/linux/mm.h
Simple merge

diff --cc mm/truncate.c
Simple merge