arm64: dts: imx8m{m,n}_venice*: add gpio-line-names

Add gpio-line-names for the various GPIO's used on Gateworks Venice
boards. Note that these GPIO's are typically 'configured' in Boot
Firmware via gpio-hog therefore we only configure line names to keep the
boot firmware configuration from changing on kernel init.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>