drm/i915/guc: enable GuC GGTT invalidation from the start

Invalidating the GuC TLBs while GuC is not loaded does not have negative
consequences, so if we're starting the driver with GuC enabled we can
use the GGTT invalidation function from the get-go, instead of switching
to it when we initialize the GuC objects.

In MTL, this fixes and issue where we try to overwrite the invalidation
function twice (once for each GuC), due to the GGTT being shared between
the primary and media GTs

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Cc: Aravind Iddamsetty <aravind.iddamsetty@intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221110175823.3867135-1-daniele.ceraolospurio@intel.com