clk: mediatek: Refine the makefile to support multiple clock drivers

Add a Kconfig to define clock configuration for each SoC, and
modify the Makefile to build drivers that only selected in config.

Signed-off-by: Shunli Wang <shunli.wang@mediatek.com>
Signed-off-by: James Liao <jamesjj.liao@mediatek.com>
Signed-off-by: Erin Lo <erin.lo@mediatek.com>
Tested-by: John Crispin <blogic@openwrt.org>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
diff --git a/drivers/clk/mediatek/Kconfig b/drivers/clk/mediatek/Kconfig
new file mode 100644
index 0000000..380c372
--- /dev/null
+++ b/drivers/clk/mediatek/Kconfig
@@ -0,0 +1,21 @@
+#
+# MediaTek SoC drivers
+#
+config COMMON_CLK_MEDIATEK
+	bool
+	---help---
+	  Mediatek SoCs' clock support.
+
+config COMMON_CLK_MT8135
+	bool "Clock driver for Mediatek MT8135"
+	select COMMON_CLK_MEDIATEK
+	default ARCH_MEDIATEK
+	---help---
+	  This driver supports Mediatek MT8135 clocks.
+
+config COMMON_CLK_MT8173
+	bool "Clock driver for Mediatek MT8173"
+	select COMMON_CLK_MEDIATEK
+	default ARCH_MEDIATEK
+	---help---
+	  This driver supports Mediatek MT8173 clocks.