gpu: ion: Add ion_page_pool.

This patch adds a new utility heaps can use to manage
memory.  In the past we have found it can be very
expensive to manage the caches when allocating memory,
but it is imposible to know whether a previous user of a
given memory allocation had a cached mapping. This patch
adds the ability to store a pool of pages that were
previously used uncached so that cache maintenance
only need be done when growing this pool.  The pool also
contains a shrinker so memory from the pool can be
recovered in low memory conditions.

Change-Id: I686fd7d192060fd32d34ef66471f62b7829006ee
Signed-off-by: Rebecca Schultz Zavin <rebecca@android.com>
Signed-off-by: Devaraj Rangasamy <dev@ti.com>

Conflicts:
	drivers/gpu/ion/ion_priv.h
gpu: ion: Fix several issues with page pool

Split out low and high mem pages so they are correctly reported
when the shrinker is called.
Fix potential deadlock caused by holding the page pool lock while
allocationg and also needing that lock from the shrink function

Change-Id: I6def3a3111f59914ef6b5b59d81a6fde37cb60c5
Signed-off-by: Rebecca Schultz Zavin <rebecca@android.com>
Signed-off-by: Devaraj Rangasamy <dev@ti.com>

Conflicts:
	drivers/gpu/ion/ion_system_heap.c
gpu: ion: Fix lockdep issue in ion_page_pool

Currently the mutex is held while kmalloc is called, under a low memory
condition this might trigger the shrinker which also takes this mutex.
Refactor so the mutex is not held during allocation.

Change-Id: Ic1d3b2f69e61209191bac84724ba56f6b98e2bc4
Signed-off-by: Rebecca Schultz Zavin <rebecca@android.com>
Signed-off-by: Devaraj Rangasamy <dev@ti.com>