input: Call keyboard's update_leds() method when the LEDs change

We should request keyboard to turn on/off its LED when detecting
any changes on the LEDs.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
Minor changes to allow this to build without CONFIG_DM_KEYBOARD:
Signed-off-by: Simon Glass <sjg@chromium.org>