drm/i915/vlv: Add drpc debugfs support for valleyview

Many of the fields from Gen6 have gone away for vlv. Strip all those
fields that are not relevent and try to update fields that we care
about. This patch give information about current RP & RC status and
individual Wells.

v2: Move Render & Media Well status to separate lines (Ville)

Signed-off-by: Deepak S <deepak.s@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>