drm/i915/uc: Improve tracking of uC init status

To be able to setup GuC submission functions during engine init we need
to commit to using GuC as soon as possible.
Currently, the only thing that can stop us from using the
microcontrollers once we've fetched the blobs is a fundamental
error (e.g. OOM); given that if we hit such an error we can't really
fall-back to anything, we can "officialize" the FW fetching completion
as the moment at which we're committing to using GuC.

To better differentiate this case, the uses_guc check, which indicates
that GuC is supported and was selected in modparam, is renamed to
wants_guc and a new uses_guc is introduced to represent the case were
we're committed to using the GuC. Note that uses_guc does still not imply
that the blob is actually loaded on the HW (is_running is the check for
that). Also, since we need to have attempted the fetch for the result
of uses_guc to be meaningful, we need to make sure we've moved away
from INTEL_UC_FIRMWARE_SELECTED.

All the GuC changes have been mirrored on the HuC for coherency.

v2: split fetch return changes and new macros to their own patches,
    support HuC only if GuC is wanted, improve "used" state
    description (Michal)

v3: s/wants_huc/uses_huc in uc_init_wopcm

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Fernando Pacheco <fernando.pacheco@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/20200218223327.11058-6-daniele.ceraolospurio@intel.com