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.
kgsl: Sync with CAF kk_2.7-stable

Signed-off-by: Sultanxda <sultanxda@gmail.com>