pinctrl: mediatek: guard sub-directory with CONFIG_PINCTRL_MTK

CONFIG_PINCTRL_MTK is more suitable than CONFIG_ARCH_MEDIATEK
to guard the drivers/pinctrl/mediatek/ directory.
(I renamed CONFIG_PINCTRL_MTK_COMMON to CONFIG_PINCTRL_MTK.)

This allows COMPILE_TEST to descend into drivers/pinctrl/mediatek
without CONFIG_ARCH_MEDIATEK define.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
diff --git a/drivers/pinctrl/Makefile b/drivers/pinctrl/Makefile
index 7ea62ef..e4bc115 100644
--- a/drivers/pinctrl/Makefile
+++ b/drivers/pinctrl/Makefile
@@ -50,4 +50,4 @@
 obj-$(CONFIG_PINCTRL_SUNXI)	+= sunxi/
 obj-$(CONFIG_PINCTRL_UNIPHIER)	+= uniphier/
 obj-$(CONFIG_ARCH_VT8500)	+= vt8500/
-obj-$(CONFIG_ARCH_MEDIATEK)	+= mediatek/
+obj-$(CONFIG_PINCTRL_MTK)	+= mediatek/