gpu: ion: Modify ION_NUM_HEAPS to reflect actual max

ION_NUM_HEAPS is meant to represent the actual max number
of heap types in the system, but currently doesn't reflect
any custom heaps.  This patch changes it to 16.

Signed-off-by: Rebecca Schultz Zavin <rebecca@android.com>
Merge remote-tracking branch 'common/android-3.0' into bfs