gralloc: add a flag for ion compatibility

 Google kernel source for hammerhead call for heap_mask instead of
  heap_id_mask, maybe other devices as well.
  This brings compatibility back without the kernel header hacks.

 To enable, set TARGET_USE_ION_COMPAT := true in the BoardConfig.mk

Change-Id: I1299b7c3e085c3597f9b512f382a416479312acb