pinctrl: add support for MediaTek MT7628

This patch adds pinctrl support for mt7628, with a file for common pinmux
functions and a file for mt7628 which has additional support for pinconf.

Signed-off-by: Weijie Gao <weijie.gao@mediatek.com>
diff --git a/drivers/pinctrl/Kconfig b/drivers/pinctrl/Kconfig
index deee924..eadcfd6 100644
--- a/drivers/pinctrl/Kconfig
+++ b/drivers/pinctrl/Kconfig
@@ -269,6 +269,7 @@
 source "drivers/pinctrl/mediatek/Kconfig"
 source "drivers/pinctrl/meson/Kconfig"
 source "drivers/pinctrl/mscc/Kconfig"
+source "drivers/pinctrl/mtmips/Kconfig"
 source "drivers/pinctrl/mvebu/Kconfig"
 source "drivers/pinctrl/nxp/Kconfig"
 source "drivers/pinctrl/renesas/Kconfig"