radeon: add initial atombios modesetting and GEM -> TTM translation layer.

radeon: add initial atombios modesetting and GEM -> TTM translation layer.

This is an initial import of the atom bios parser with modesetting support
for r500 hw using atombios. It also includes a simple memory manager
layer that translates a radeon GEM style interface onto TTM internally.

So far this memory manager has only been used for pinned object allocation
for the DDX to test modesetting.