drm/xe/uc: Rename guc_submission_enabled() to uc_enabled()

The guc_submission_enabled() function is being used as a boolean toggle
for all firmwares and all related features, not just GuC submission. We
could add additional flags/functions to distinguish and allow different
use-cases (e.g. loading HuC but not using GuC submission), but given
that not using GuC is a debug-only scenario having a global switch for
all FWs is enough. However, we want to make it clear that this switch
turns off everything, so rename it to uc_enabled().

v2: rebase on s/XE_WARN_ON/xe_assert

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: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>