gpu: ion: Modify reserve function for carveouts with no start address

This patch allows you to specify a heap that requires carveout memory
but that doesn't specify a start address.  Memblock_alloc will be called
to find a location for these heaps.

Change-Id: I9c79b30e3105e796060fc74b058f04093ee5e96e
Signed-off-by: Rebecca Schultz Zavin <rebecca@android.com>
gpu: ion: Fix bug where MAP ioctl was no longer supported

Change-Id: Idbe628ed7dbd6a14469194120b94934d6e99d367
Signed-off-by: Rebecca Schultz Zavin <rebecca@android.com>
gpu: ion: Switch heap rbtree to a prio list

Switches the rbtree tree of heaps for a plist.  This significantly
simplifies the code and the list is small and is modified only at
first boot so the rbtree is unnecessary.  This also switches
the traversal of the heap list to traverse from highest to lowest
id's.  This allows allocations to pass a heap mask that falls
back on the system heap -- typically id 0, which is the common case.

Change-Id: I715be6f4cf020a84ca4f1947c30ee3d2559fb523
Signed-off-by: Rebecca Schultz Zavin <rebecca@android.com>