ARM: dts: imx6q-dhcom: Add keys and leds to the PDK2 board

On the PDK2 there are 4 keys and 4 leds. DHCOM GPIOs are
used for that, but one led isn't useable, because the GPIO
is already used as touch interrupt.

Signed-off-by: Christoph Niedermaier <cniedermaier@dh-electronics.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Fabio Estevam <festevam@denx.de>
Cc: Marek Vasut <marex@denx.de>
Cc: NXP Linux Team <linux-imx@nxp.com>
Cc: kernel@dh-electronics.com
To: linux-arm-kernel@lists.infradead.org
Signed-off-by: Shawn Guo <shawnguo@kernel.org>