intel: fix stall debug option

Missing the parsing bit.

Fixes: 317512e038 ("anv/intel: add a new debug flag for stalling after every draw/dispatch")
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16338>

src/intel/dev/intel_debug.c

@@ -93,6 +93,7 @@ static const struct debug_control debug_control[] = {
    { "rt",          DEBUG_RT },
    { "task",        DEBUG_TASK },
    { "mesh",        DEBUG_MESH },
+   { "stall",       DEBUG_STALL },
    { NULL,    0 }
 };