Move gpio_debug from board to EC code

The gpio_debug() functionality depends on the ITE registers and not
anything board-specific.

Signed-off-by: Tim Crawford <tcrawford@system76.com>

src/board/system76/lemp9/include/board/gpio.h

@@ -6,7 +6,6 @@
 #include <ec/gpio.h>
 
 void gpio_init(void);
-void gpio_debug(void);
 
 // clang-format off
 extern struct Gpio __code ACIN_N;