clocksource/drivers/nspire: Add the COMPILE_TEST option

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

A new Kconfig option is added, CONFIG_NSPIRE_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-nspire/Kconfig

@@ -7,5 +7,6 @@ config ARCH_NSPIRE
 	select ARM_AMBA
 	select ARM_VIC
 	select ARM_TIMER_SP804
+	select NSPIRE_TIMER
 	help
 	  This enables support for systems using the TI-NSPIRE CPU

drivers/clocksource/Kconfig

@@ -199,6 +199,13 @@ config U300_TIMER
 	help
 	  Enables support for the U300 timer.
 
+config NSPIRE_TIMER
+	bool "NSpire timer driver" if COMPILE_TEST
+	depends on GENERIC_CLOCKEVENTS
+	select CLKSRC_MMIO
+	help
+	  Enables support for the Nspire timer.
+
 config CLKSRC_DBX500_PRCMU_SCHED_CLOCK
 	bool "Clocksource PRCMU Timer sched_clock"
 	depends on (CLKSRC_DBX500_PRCMU && !CLKSRC_NOMADIK_MTU_SCHED_CLOCK)

drivers/clocksource/Makefile

@@ -32,7 +32,7 @@ obj-$(CONFIG_SUN5I_HSTIMER)	+= timer-sun5i.o
 obj-$(CONFIG_MESON6_TIMER)	+= meson6_timer.o
 obj-$(CONFIG_TEGRA_TIMER)	+= tegra20_timer.o
 obj-$(CONFIG_VT8500_TIMER)	+= vt8500_timer.o
-obj-$(CONFIG_ARCH_NSPIRE)	+= zevio-timer.o
+obj-$(CONFIG_NSPIRE_TIMER)	+= zevio-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