misc: Add support for PMEM ADSP (overriding ION).

Some devices require PMEM to do VIDC or Camera allocations, enable this to
conditionally disable ION support on these targets.

Change-Id: I62a7e375dace6df761764e3d67efc483bd1e99ba
jenad: adjust defconfig for PMEM_ADSP

Change-Id: I6ad2e4824b48beb970c04862561136146d161e7e