clocksource/drivers/prima2: Add the COMPILE_TEST option

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

A new Kconfig option is added, CONFIG_PRIMA2_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-prima2/Kconfig

@@ -39,6 +39,7 @@ config ARCH_PRIMA2
 	default y
 	select SIRF_IRQ
 	select ZONE_DMA
+	select PRIMA2_TIMER
 	help
           Support for CSR SiRFSoC ARM Cortex A9 Platform