clocksource: Add Freescale FlexTimer Module (FTM) timer support

The Freescale FlexTimer Module time reference is a 16-bit counter
that can be used as an unsigned or signed increase counter.

CNTIN defines the starting value of the count and MOD defines the
final value of the count. The value of CNTIN is loaded into the FTM
counter, and the counter increments until the value of MOD is reached,
at which point the counter is reloaded with the value of CNTIN. That's
also when an overflow interrupt will be generated.

Here using the 'evt' prefix or postfix as clock event device and
the 'src' as clock source device.

Signed-off-by: Xiubo Li <Li.Xiubo@freescale.com>
Cc: Shawn Guo <shawn.guo@linaro.org>
Cc: Jingchang Lu <b35083@freescale.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index 96918e1..0437767 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -136,6 +136,11 @@
 	  for all devicetree enabled platforms. This driver will be
 	  needed only on systems that do not have the Exynos MCT available.
 
+config FSL_FTM_TIMER
+	bool
+	help
+	  Support for Freescale FlexTimer Module (FTM) timer.
+
 config VF_PIT_TIMER
 	bool
 	help