i8253: Create common clockevent implementation

arm, mips and x86 implement i8253 based clockevents. All the same code
copied. Create a common implementation in drivers/clocksource/i8253.c.

About time to rename drivers/clocksource/ to something else.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: John Stultz <john.stultz@linaro.org>
Link: http://lkml.kernel.org/r/20110609130621.921710458@linutronix.de

diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index 330343b..d8d3e02 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -1,11 +1,14 @@
 config CLKSRC_I8253
 	bool
 
+config CLKEVT_I8253
+	bool
+
 config I8253_LOCK
 	bool
 
 config CLKBLD_I8253
-	def_bool y if CLKSRC_I8253 || I8253_LOCK
+	def_bool y if CLKSRC_I8253 || CLKEVT_I8253 || I8253_LOCK
 
 config CLKSRC_MMIO
 	bool