ARM: dts: imx7-colibri: add gpio-line-names

Add Colibri SODIMM numbers as GPIO line names on module level. The GPIO
lines with a name are all available on the SODIMM edge connector of the
Colibri iMX7 module and therefore a customer might use it as a GPIO. The
Toradex Evaluation Board has the SODIMM numbers printed on the silk-
screen. This allows a customer to quickly control a GPIO on a pin-header
by using the name printed next to it.

Putting the GPIO line name on module level makes sure that a customer
gets a reasonable default. If more meaningful names are available on a
custom carrier board, the user can overwrite the line names in a carrier
board level device tree.

The eMMC based modules share all GPIO names except two GPIOs on bank 6
which are not available on the raw NAND devices. Hence overwrite GPIO
line names of bank 6 in the eMMC specific device tree file.

Signed-off-by: Stefan Agner <stefan.agner@toradex.com>
Reviewed-by: Philippe Schenker <philippe.schenker@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>