ARM: dts: imx: bx50v3: Define GPIO line names

Define GPIO line names for b450v3, b650v3, and b850v3.

Signed-off-by: Ian Ray <ian.ray@ge.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>