gma500: GEM and GEM glue

The driver uses GEM along with a couple of small bits of wrapping of its
own. The only real oddity here is the support for using the 'stolen' memory
rather than wasting several MB.

We use a simple resource manager as we don't need to manage our space
intensively at all as we only do 2D work. We also have a GTT which is
entirely GPU facing so in the Cedarview case are not even allocating from
host address space.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>