ARM: bcm2835: make use of CLKSRC_OF

Using CLKSRC_OF enables deletion of the SoC-specific header
bcm2835_timer.h, replacing the custom function bcm2835_timer_init() with
the standardized automatic clocksource_of_init().

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 67874b8..670cf44 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -344,6 +344,7 @@
 	select ARM_ERRATA_411920
 	select ARM_TIMER_SP804
 	select CLKDEV_LOOKUP
+	select CLKSRC_OF
 	select COMMON_CLK
 	select CPU_V6
 	select GENERIC_CLOCKEVENTS