bring back pmem/ashmem allocators

o removed RefBase usages
o ifdef for TARGET_USES_ION

Change-Id: Ief331f4c847b86be0e37d24983097af1f53234a2

Conflicts:
	common.mk
	libcopybit/copybit.cpp
	libgralloc/Android.mk
	libgralloc/gralloc_priv.h