ARM: mxc: Add sched_clock to mxc platform

Add sched_clock using cyc_to_sched_clock and update_sched_clock
with HAVE_SCHED_CLOCK
tested on iMX27 and iMX35

Signed-off-by: Jan Weitzel <j.weitzel@phytec.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 599e163..f4027ab 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -362,6 +362,7 @@
 	select GENERIC_CLOCKEVENTS
 	select ARCH_REQUIRE_GPIOLIB
 	select CLKDEV_LOOKUP
+	select HAVE_SCHED_CLOCK
 	help
 	  Support for Freescale MXC/iMX-based family of processors