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>
diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
index 008d8a0..df99c92 100644
--- a/drivers/clocksource/Makefile
+++ b/drivers/clocksource/Makefile
@@ -33,7 +33,7 @@
 obj-$(CONFIG_TEGRA_TIMER)	+= tegra20_timer.o
 obj-$(CONFIG_VT8500_TIMER)	+= vt8500_timer.o
 obj-$(CONFIG_ARCH_NSPIRE)	+= zevio-timer.o
-obj-$(CONFIG_ARCH_BCM_MOBILE)	+= bcm_kona_timer.o
+obj-$(CONFIG_BCM_KONA_TIMER)	+= bcm_kona_timer.o
 obj-$(CONFIG_CADENCE_TTC_TIMER)	+= cadence_ttc_timer.o
 obj-$(CONFIG_CLKSRC_EFM32)	+= time-efm32.o
 obj-$(CONFIG_CLKSRC_STM32)	+= timer-stm32.o