nitrogen6x: add missing pinctrl to fix mmc

Since commit f7ac30b042d, the pin muxing for mmc was removed from the
board file to be managed by DM_MMC which requires PINCTRL to work. It
made the change for sabrelite but nitrogen configs were forgotten.

Signed-off-by: Gary Bisson <gary.bisson@boundarydevices.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Acked-by: Troy Kisky <troy.kisky@boundarydevices.com>
diff --git a/configs/nitrogen6s1g_defconfig b/configs/nitrogen6s1g_defconfig
index 8b720b0..17133c5 100644
--- a/configs/nitrogen6s1g_defconfig
+++ b/configs/nitrogen6s1g_defconfig
@@ -68,6 +68,8 @@
 CONFIG_PHY_MICREL_KSZ90X1=y
 CONFIG_FEC_MXC=y
 CONFIG_MII=y
+CONFIG_PINCTRL=y
+CONFIG_PINCTRL_IMX6=y
 CONFIG_MXC_UART=y
 CONFIG_SPI=y
 CONFIG_DM_SPI=y