ANDROID: staging: ion: add support for consistent heap ids

heap id is part of ION's UAPI. Since the heaps are now kernel modules,
the current scheme of incrementing the heap id for the next heap doesn't
work. For example, if one insert->remove->insert the system heap module,
the heap id associated with the system heap changes. This immediately
breaks all of userspace.

So, in order to fix this, we reserve first 16 heap ids for GKI heaps
and leave 16 more heap ids for any custom heap type that may exist.

Bug: 133508579
Test: ion-unit-test
Test: ion-unit-test (after removal and insertion of system heap module)

Change-Id: I8412e590263869e029151a017b072399f54206f0
Signed-off-by: Sandeep Patil <sspatil@google.com>