drm/i915/huc: stall media submission until HuC is loaded

Wait on the fence to be signalled to avoid the submissions finding HuC
not yet loaded.

v2: use dedicaded wait_queue_entry for waiting in HuC load, as submitq
can't be re-used for it.

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Tony Ye <tony.ye@intel.com>
Acked-by: Tony Ye <tony.ye@intel.com>
Reviewed-by: Alan Previn <alan.previn.teres.alexis@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220928004145.745803-13-daniele.ceraolospurio@intel.com