drivers: dma-removed: Don't free prohibited memmap entries

The mm subsystem access page structs aligned to
pageblock_nr_pages and assumes that these are valid. We
must not free any memmap entries that it may inspect.

CRs-Fixed: 1000343
Change-Id: I73e0402ee72cad8df307ece1134f9e7304125cf6
Signed-off-by: Shiraz Hashim <shashim@codeaurora.org>