drm/xe/uc: Fix uC status tracking

The current uC status tracking has a few issues:

1) the HuC is moved to "disabled" instead of "not supported"

2) the status is left uninitialized instead of "disabled" when the
   modparam is used to disable support

3) due to #1, a number of checks are done against "disabled" instead of
   the appropriate status.

Address all of those by making sure to follow the appropriate state
transition and checking against the required state.

v2: rebase on s/guc_submission_enabled/uc_enabled/

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>