ARM: dts: AM33XX: Add pinctrl binding to gpio-leds node

Now gpio-leds driver is using devm_pinctrl_get_select_default()
api to set default pinmux configuration required for the
functionality of the driver, so this patch moves respective
pinctrl binding inside leds node.

Signed-off-by: Vaibhav Hiremath <hvaibhav@ti.com>
Signed-off-by: Benoit Cousson <benoit.cousson@linaro.org>