clk: Hi6220: separately build stub clock driver

The previous code, kernel builds Hi6220's common clock driver and stub
clock driver together. Stub clock driver has introduced the dependency
with CONFIG_MAILBOX, so kernel will not build Hi6220's common clock
driver due ARM64's defconfig have not enabled CONFIG_MAILBOX by default.

So separately build stub clock driver and common clock driver for
Hi6220; and only let stub clock driver has the dependency with
CONFIG_MAILBOX.
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Tested-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>

drivers/clk/hisilicon/Kconfig

 config COMMON_CLK_HI6220
 	bool "Hi6220 Clock Driver"
-	depends on (ARCH_HISI || COMPILE_TEST) && MAILBOX
+	depends on ARCH_HISI || COMPILE_TEST
 	default ARCH_HISI
 	help
 	  Build the Hisilicon Hi6220 clock driver based on the common clock framework.
+
+config STUB_CLK_HI6220
+	bool "Hi6220 Stub Clock Driver"
+	depends on COMMON_CLK_HI6220 && MAILBOX
+	help
+	  Build the Hisilicon Hi6220 stub clock driver.

drivers/clk/hisilicon/Makefile

@@ -7,4 +7,5 @@ obj-y	+= clk.o clkgate-separated.o clkdivider-hi6220.o
 obj-$(CONFIG_ARCH_HI3xxx)	+= clk-hi3620.o
 obj-$(CONFIG_ARCH_HIP04)	+= clk-hip04.o
 obj-$(CONFIG_ARCH_HIX5HD2)	+= clk-hix5hd2.o
-obj-$(CONFIG_COMMON_CLK_HI6220)	+= clk-hi6220.o clk-hi6220-stub.o
+obj-$(CONFIG_COMMON_CLK_HI6220)	+= clk-hi6220.o
+obj-$(CONFIG_STUB_CLK_HI6220)	+= clk-hi6220-stub.o