security: pfk: use page_mapping to avoid wrong memory access

This patch fixes potentially wrong memory access when doing ICE operations.

Change-Id: I4893d106877f6313bbcd2218d7c4ad12f63a0cbe
Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>
Signed-off-by: Neeraj Soni <neersoni@codeaurora.org>