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.

diff --git a/drivers/pinctrl/mtmips/Kconfig b/drivers/pinctrl/mtmips/Kconfig
new file mode 100644
index 0000000..8482a38
--- /dev/null
+++ b/drivers/pinctrl/mtmips/Kconfig
@@ -0,0 +1,13 @@
+
+config PINCTRL_MTMIPS
+	depends on ARCH_MTMIPS
+	bool
+
+config PINCTRL_MT7628
+	bool "MediaTek MT7628 pin control driver"
+	select PINCTRL_MTMIPS
+	depends on SOC_MT7628 && PINCTRL_GENERIC
+	help
+	  Support pin multiplexing control on MediaTek MT7628.
+	  The driver is controlled by a device tree node which contains
+	  the pin mux functions for each available pin groups.