drm/i915/skl: Print the DMC firmware status in debugfs

drm/i915/skl: Print the DMC firmware status in debugfs

Create a new debufs file for it, we'll have a few more things to add
there.

v2: Fix checkpatch warning about static const array
v3: use named initializers (Ville)
v4: strip out csr_state as it will be removed in future (Ville, Imre)

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com> (v1)
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1445950025-5793-3-git-send-email-mika.kuoppala@intel.com
Reviewed-by: Imre Deak <imre.deak@intel.com>
Tested-by: Daniel Stone <daniels@collabora.com> # SKL
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>