drm/i915: extract ums suspend/resume into i915_ums.c

Similarly to how i915_dma.c is shaping up to be the dungeon hole for
all things supporting dri1, create a new one to hide all the crazy
things which are only really useful for ums support. Biggest part is
the register suspend/resume support.

Unfortunately a lot of it is still intermingled with bits and pieces
we might still need, so needs more analysis and needs to stay in
i915_suspend.c for now.

Reviewed-by: Imre Deak <imre.deak@intel.com>

v2: s/modeset_reg/display_reg/ as suggested by Imre, to avoid
confusion between the kernel modeset code and display save/restore to
support ums.

v3: Fixup alphabetical order in the Makefile, spotted by Chris Wilson.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
index 0f2c549..91f3ac6 100644
--- a/drivers/gpu/drm/i915/Makefile
+++ b/drivers/gpu/drm/i915/Makefile
@@ -16,6 +16,7 @@
 	  i915_gem_tiling.o \
 	  i915_sysfs.o \
 	  i915_trace_points.o \
+	  i915_ums.o \
 	  intel_display.o \
 	  intel_crt.o \
 	  intel_lvds.o \