keymaster: 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: I8be2f1f001a909689074e1ccc7b34ab980776638