drm/i915/uc: introduce intel_uc_fw_supported

Instead of always checking in the device config is GuC and HuC are
supported or not, we can save the state in the uc_fw structure and
avoid going through i915 every time from the low-level uc management
code. while at it FIRMWARE_NONE has been renamed to better indicate that
we haven't started the fetch/load yet, but we might have already selected
a blob.

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190713100016.8026-3-chris@chris-wilson.co.uk
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>