This changes ensures device is active when frequency limits are changed.
This is needed as we are writing to register RPNSWREQ in intel_set_rps.
If not done, might lead to undesired errors like:
[ 1965.189137] [drm:fw_domains_get] *ERROR* blitter: timed out waiting for forcewake ack to clear.

v2: Added elaborate commit message. (Jani)
    Fixing RPM reference drop in early exit paths. (Ville)
Signed-off-by: Sagar Arun Kamble <sagar.a.kamble@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1454951831-11778-1-git-send-email-sagar.a.kamble@intel.comSigned-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>