ARM: tegra: move timer.c to drivers/clocksource/

Move arch/arm/mach-tegra/timer.c to drivers/clocksource/tegra20_timer.c
so that the code is co-located with other clocksource drivers, and to
reduce the size of the mach-tegra directory.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 67874b8..eb9fc2f 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -642,6 +642,7 @@
 	select ARCH_HAS_CPUFREQ
 	select CLKDEV_LOOKUP
 	select CLKSRC_MMIO
+	select CLKSRC_OF
 	select COMMON_CLK
 	select GENERIC_CLOCKEVENTS
 	select GENERIC_GPIO