drm/gma500: Hook up the MMU

Properly init the MMU and add MMU entries when adding GTT entries

Signed-off-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>

diff --cc drivers/gpu/drm/gma500/gtt.c
Simple merge

diff --cc drivers/gpu/drm/gma500/psb_drv.c
Simple merge