clocksource/drivers/bcm_kona: Add the COMPILE_TEST option

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

A new Kconfig option is added, CONFIG_BCM_KONA_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/mach-bcm/Kconfig

@@ -89,6 +89,7 @@ config ARCH_BCM_MOBILE
 	select HAVE_ARM_ARCH_TIMER
 	select PINCTRL
 	select ARCH_BCM_MOBILE_SMP if SMP
+	select BCM_KONA_TIMER
 	help
 	  This enables support for systems based on Broadcom mobile SoCs.