drm/i915: Add csr programming registers to dmc debugfs entry

drm/i915: Add csr programming registers to dmc debugfs entry

We check these to determine firmware loading status. Include
them to help to debug causes of firmware loading fails.

v2: Move all CSR specific registers to i915_reg.h (Ville)
v3: Rebase
v4: Rebase (RPM ref)

Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1446220487-32691-1-git-send-email-mika.kuoppala@intel.com
Tested-by: Daniel Stone <daniels@collabora.com> # SKL
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>