ARM: imx: reset_controller may be disabled

The new reset controller API is optional, so if that is disabled,
we must not call it from platform code.

arch/arm/mach-imx/built-in.o: In function
 `imx_src_init': /git/arm-soc/arch/arm/mach-imx/src.c:144:
	undefined reference to `reset_controller_register'

Cc: Sascha Hauer <kernel@pengutronix.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/arm/mach-imx/src.c

@@ -138,6 +138,7 @@ void __init imx_src_init(void)
 	WARN_ON(!src_base);
 
 	imx_reset_controller.of_node = np;
+	if (IS_ENABLED(CONFIG_RESET_CONTROLLER))
 		reset_controller_register(&imx_reset_controller);
 
 	/*