Add a flag to skip waiting for safe mode

Sometimes we don't want the delay in the device's startup.

I used a simple flag, but now it also occurs to me that we could
instead make the wait time a define, and set it to 0 to disable it.

frozen/circuitpython-stage

@@ -1 +1 @@
-Subproject commit 275c03e340c3853ab1c53fc15b6df07ceb672bdc
+Subproject commit d0f1c46d7f879cd60562ee69900d619499d4d206

supervisor/shared/safe_mode.c

@@ -66,6 +66,9 @@ safe_mode_t wait_for_safe_mode_reset(void) {
         reset_reason != RESET_REASON_SOFTWARE) {
         return NO_SAFE_MODE;
     }
+    #ifdef CIRCUITPY_SKIP_SAFE_MODE_WAIT
+    return NO_SAFE_MODE;
+    #endif
     port_set_saved_word(SAFE_MODE_DATA_GUARD | (MANUAL_SAFE_MODE << 8));
     // Wait for a while to allow for reset.