drm/radeon: embed struct drm_gem_object

Unconditionally initialize the drm gem object - it's not
worth the trouble not to for the few kernel objects.

This patch only changes the place of the drm gem object,
access is still done via pointers.

v2: Uncoditionally align the size in radeon_bo_create. At
least the r600/evergreen blit code didn't to this, angering
the paranoid gem code.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>