drm/i915/uc: Unify uC platform check

We have several HAS_* checks for GuC and HuC but we mostly use HAS_GUC
and HAS_HUC, with only 1 exception. Since our HW always has either
both uC or neither of them, just replace all the checks with a unified
HAS_UC.

v2: use HAS_GT_UC (Michal)
v3: fix comment (Michal)

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190725001813.4740-2-daniele.ceraolospurio@intel.com