drm/i915/uc: Add init_fw/fini_fw to to intel_uc_ops

Firmware fetching and cleanup steps are only meaningful if we are
running with uC enabled. Make these functions part of the uc_ops.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200110222723.14724-3-michal.wajdeczko@intel.com