drm/i915/dg2: wait for HuC load completion before running selftests

On DG2, submissions to VCS engines tied to a gem context are blocked
until the HuC is loaded. Since some selftests do use a gem context,
wait for the HuC load to complete before running the tests to avoid
contamination.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/10564
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240410201505.894594-1-daniele.ceraolospurio@intel.com