gma500: begin adding GEM

This puts in place the infrastructure for GEM allocators. Our implementation
is fairly simplistic at this point and we don't deal with things like
evicting objects from the GART to make space, nor compaction.

We extent our gtt_range struct to include a GEM object and that allows GEM
to do all the handle management and most of the memory mapping work for us.

This patch also doesn't load GEM pages into the GART so the GEM side isn't
very useful. Before we can do that a fair bit of work is needed reworking the
internal GTT code.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>