ARM: dts: lan966x: kontron-d10: fix SPI CS

ARM: dts: lan966x: kontron-d10: fix SPI CS

[ Upstream commit fcb79ee3f0b15ed15f35eca5f24e952fdced9c61 ]

The pinctrl node was missing which change the pin mux to GPIO mode.
Add it so we don't have to rely on the bootloader to set the correct
mode.

Fixes: 79d83b3a458e ("ARM: dts: lan966x: add basic Kontron KSwitch D10 support")
Signed-off-by: Michael Walle <mwalle@kernel.org>
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20230616-feature-d10-dt-cleanups-v1-2-50dd0452b8fe@kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>