gralloc4: sync ion buffers around CPU usage

mali_gralloc_ion_sync is called if BOARD_USES_GRALLOC_ION_SYNC is set,
but currently the implementation is empty.  Added an implementation that
passes through to libdmabufheap's sync interface.

Test: Set camera permissions to "Ask every time"; reboot; launch camera
Test: RealCalc
Fixes: 185289225
Fixes: 186613737
Fixes: 183735780
Change-Id: I8425d2d94c0202fa2dabf8ff60d66bc8d40b6b86
1 file changed