drm/i915/skl: Store and print the DMC firmware version we load

drm/i915/skl: Store and print the DMC firmware version we load

That can be handy later on to tell which DMC firmware version the user
has, by just looking at the dmesg.

v2: use DRM_DEBUG_DRIVER (Chris)
v3: use DRM_INFO (Marc Herbert)

Cc: Marc Herbert <marc.herbert@intel.com>
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/1445950025-5793-1-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>