drm/i915/uc: consolidate firmware cleanup

We are quite trigger happy in cleaning up the firmware blobs, as we do
so from several error/fini paths in GuC/HuC/uC code. We do have the
__uc_cleanup_firmwares cleanup function, which unwinds
__uc_fetch_firmwares and is already called both from the error path of
gem_init and from gem_driver_release, so let's stop cleaning up from
all the other paths.

The fact that we're not cleaning the firmware immediately means that
we can't consider firmware availability as an indication of
initialization success. A "LOADABLE" status has been added to
indicate that the initialization was successful, to be used to
selectively load HuC only if HuC init has completed (HuC init failure
is not considered a fatal error).

v2: s/ready_to_load/loadable (Michal), only run guc/huc_fini if the
    fw is in loadable state

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com> #v1
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200218223327.11058-9-daniele.ceraolospurio@intel.com