Revert "add'l file from previous commit"

This reverts commit 2c4011722770a2af206920def525b502d52c8e35.
Revert "gpu: ion: Add support for specifying a default prefetch size"

This reverts commit 3281b936bfc937afe286429842b0aae34a353b1f.
gpu: ion: Add ioctls for prefetching/draining pools

Multiple heaps in Ion are begining to pool large amounts of memory.
This gives a boost on average but clients may still take a hit
if the pool needs to be filled up again. Add an ioctl to give a
'hint' to add memory to the pool. Equivalently, add an ioctl to
drain some of the memory out of the pool to ennsure the memory
isn't hanging around for too long.

Change-Id: I2974322caa1520fd199d9cf2658f2fafceffb65c
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>