clocksource/drivers/clps_711x: Add the COMPILE_TEST option

Change the Kconfig option logic to fullfil with the current approach.

A new Kconfig option is added, CONFIG_CLPS711X_TIMER and is selected by the
platform. Then the clocksource's Kconfig is changed to make this option
selectable by the user if the COMPILE_TEST option is set. Otherwise, it is
up to the platform's Kconfig to select the timer.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

arch/arm/Kconfig

@@ -358,10 +358,10 @@ config ARCH_CLPS711X
 	bool "Cirrus Logic CLPS711x/EP721x/EP731x-based"
 	select ARCH_REQUIRE_GPIOLIB
 	select AUTO_ZRELADDR
-	select CLKSRC_MMIO
 	select COMMON_CLK
 	select CPU_ARM720T
 	select GENERIC_CLOCKEVENTS
+	select CLPS711X_TIMER
 	select MFD_SYSCON
 	select SOC_BUS
 	help