drm/i915: Merge i915_dma.c into i915_drv.c

i915_dma.c used to contain the DRI1/UMS horror show, but now all that
remains are the out-of-place driver level interfaces (such as
allocating, initialising and registering the driver). These should be in
i915_drv.c alongside similar routines for suspend/resume.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1466773227-7994-10-git-send-email-chris@chris-wilson.co.uk