platform: msm_shared: Fixed inconsistent cache issue for mmc

DMA onto write back memory is unsafe/nonportable, but callers to
mmc_read routine normally provide write back buffers.
Add invalidate cache function to flush cache to DDR,
when LK memory is configured as write back.

Change-Id: I5770e7ba5b3dbcb9c08efe94ad9f13a8f3cca48c
1 file changed