ANDROID: dma-buf: heaps: Allow cma heaps to be configured as a module

Allow loading cma heap as a module instead of just as a
statically built in heap.

Since there isn't a good mechanism for dmabuf lifetime tracking
it isn't safe to allow the heap drivers to be unloaded, so these
drivers do not implement any module unloading functionality and
will show up in lsmod as "[permanent]".

[cmllamas: reapply https://r.android.com/1422536

 after pulling dma-buf
 updates from upstream mainline but drop the now obsolete symbol exports
 and fix up the commit log accordingly]

Signed-off-by: John Stultz <john.stultz@linaro.org>

Bug: 155218010
Cc: John Stultz <jstultz@google.com>
Cc: T.J. Mercier <tjmercier@google.com>
Link: https://lore.kernel.org/lkml/20191025234834.28214-3-john.stultz@linaro.org/


Merged-In: I8d4516899d42c0b6e145bde8a0fed1235ae46654
Change-Id: Ie8a24ff7dd808b9eddaddce56244f0344f427f08
Signed-off-by: Hridya Valsaraju <hridya@google.com>
Signed-off-by: Carlos Llamas <cmllamas@google.com>