clocksource/drivers/st_lpc: Add the COMPILE_TEST option

Increase the compilation test coverage by adding the COMPILE_TEST option.
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

drivers/clocksource/Kconfig

@@ -325,7 +325,7 @@ config CLKSRC_IMX_GPT
 	select CLKSRC_MMIO
 
 config CLKSRC_ST_LPC
-	bool
+	bool "Low power clocksource found in the LPC" if COMPILE_TEST
 	select CLKSRC_OF if OF
 	help
 	  Enable this option to use the Low Power controller timer