Revert "firmware: Make interrupt signal shorter (10us)"

The longer duration is actually required, likely due to debouncing
applied on the SoC side. Even 50us was unreliable.

This reverts commit 3b723583e7.

firmware/main.c

@@ -2082,7 +2082,7 @@ void main(void)
 
 				// signal interrupt
 				ext_int_assert();
-				delay_us(10);
+				delay_us(100);
 				ext_int_deassert();
 #if CONFIG_USB_STACK
 				usb_key_change = 1;