omap: Add TILER reservation ION heap to omap4 board file

registration gives ion clients access to tiler reservation heap

The tiler reservation heap is for allocating TILER address space, but
not the underlying pages.  The idea is to allocate TILER address space
and one or more ION buffers from the system heap, and map system heap
buffers into the allocated TILER address space.

Signed-off-by: David Schleef <ds@ti.com>
Change-Id: I3eb8125d604106185c37f75d61cbbd9f2ef175a1