clocksource: sti: Provide support for the ST LPC Clocksource IP

This IP is shared with Watchdog and RTC functionality.  All 3 of
these devices are mutually exclusive from one another i.e. Only 1
IP can be used at any given time.  We use the device-driver model
combined with a DT 'mode' property to enforce this.

The ST LPC Clocksource IP can be used as the system (tick) timer.

Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index 4e57730..ae3ec9d 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -293,4 +293,12 @@
 	depends on ARM && CLKDEV_LOOKUP
 	select CLKSRC_MMIO
 
+config CLKSRC_ST_LPC
+	bool
+	depends on ARCH_STI
+	select CLKSRC_OF if OF
+	help
+	  Enable this option to use the Low Power controller timer
+	  as clocksource.
+
 endmenu