drm/i915: Add more keywords to firmware loading message

To find out what firmware we actually loaded (from dmesg) the explicit
'dmc' and 'firmware' are missing from the info printout. Add them.

Cc: Imre Deak <imre.deak@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1479288806-17355-1-git-send-email-mika.kuoppala@intel.com