clk: samsung: allow building the clkout driver as module

The Exynos clock output driver can be built as module (it does not have
to be part of core init process) for better customization.  Adding a
KConfig entry allows also compile testing for build coverage.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Chanwoo Choi <cw00.choi@samsung.com>
Acked-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Link: https://lore.kernel.org/r/20201110193749.261367-1-krzk@kernel.org

drivers/clk/samsung/Kconfig

@@ -19,6 +19,16 @@ config EXYNOS_AUDSS_CLK_CON
 	  on some Exynos SoC variants. Choose M or Y here if you want to
 	  use audio devices such as I2S, PCM, etc.
 
+config EXYNOS_CLKOUT
+	tristate "Samsung Exynos clock output driver"
+	depends on COMMON_CLK_SAMSUNG
+	default y if ARCH_EXYNOS
+	help
+	  Support for the clock output (XCLKOUT) present on some of Exynos SoC
+	  variants. Usually the XCLKOUT is used to monitor the status of the
+	  certains clocks from SoC, but it could also be tied to other devices
+	  as an input clock.
+
 # For S3C24XX platforms, select following symbols:
 config S3C2410_COMMON_CLK
 	bool "Samsung S3C2410 clock controller support" if COMPILE_TEST

drivers/clk/samsung/Makefile

@@ -15,7 +15,7 @@ obj-$(CONFIG_SOC_EXYNOS5420)	+= clk-exynos5420.o
 obj-$(CONFIG_SOC_EXYNOS5420)	+= clk-exynos5-subcmu.o
 obj-$(CONFIG_EXYNOS_ARM64_COMMON_CLK)	+= clk-exynos5433.o
 obj-$(CONFIG_EXYNOS_AUDSS_CLK_CON) += clk-exynos-audss.o
-obj-$(CONFIG_ARCH_EXYNOS)	+= clk-exynos-clkout.o
+obj-$(CONFIG_EXYNOS_CLKOUT)	+= clk-exynos-clkout.o
 obj-$(CONFIG_EXYNOS_ARM64_COMMON_CLK)	+= clk-exynos7.o
 obj-$(CONFIG_S3C2410_COMMON_CLK)+= clk-s3c2410.o
 obj-$(CONFIG_S3C2410_COMMON_DCLK)+= clk-s3c2410-dclk.o

drivers/clk/samsung/clk-exynos-clkout.c

@@ -72,6 +72,7 @@ static const struct of_device_id exynos_clkout_ids[] = {
 		.data = &exynos_clkout_exynos5,
 	}, { }
 };
+MODULE_DEVICE_TABLE(of, exynos_clkout_ids);
 
 /*
  * Device will be instantiated as child of PMU device without its own