ARM: dts: imx6ull-colibri: add gpio-line-names

Add GPIO line names on module-level. Those are all GPIOs that a user
might use on his custom carrier board. If more meaningful names are
available on the carrier board, the user can overwrite the line names
in the carrier board-level device tree.

Signed-off-by: Oleksandr Suvorov <oleksandr.suvorov@toradex.com>
Signed-off-by: Denys Drozdov <denys.drozdov@toradex.com>
Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>