ARM: dts: imx6q-dhcom: Fill GPIO line names on DHCOM SoM

ARM: dts: imx6q-dhcom: Fill GPIO line names on DHCOM SoM

Fill in the custom GPIO line names used by DH on the DHCOM SoM.
The GPIO line names are in accordance to DHCOM Design Guide R04
available at [1], section 3.9 GPIO. Adding also GPIO line names
for the hardware and memory coding.

[1] https://wiki.dh-electronics.com/images/5/52/DOC_DHCOM-Design-Guide_R04_2018-06-28.pdf

Signed-off-by: Christoph Niedermaier <cniedermaier@dh-electronics.com>
Reviewed-by: Marek Vasut <marex@denx.de>
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>