ARM: imx: move timer driver into drivers/clocksource

After the cleanup on imx timer driver, now it's ready to be moved into
drivers/clocksource/.  Let's do it.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index 51d7865f..618102e 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -258,4 +258,10 @@
 	help
 	  This enables OST0 support available on PXA and SA-11x0
 	  platforms.
+
+config CLKSRC_IMX_GPT
+	bool "Clocksource using i.MX GPT" if COMPILE_TEST
+	depends on ARM && CLKDEV_LOOKUP
+	select CLKSRC_MMIO
+
 endmenu