This is based upon both arch/arm/mach-footbridge/isa-timer.c and
arch/x86/kernel/i8253.c.

Acked-by: John Stultz
Acked-by: Thomas Gleixner
Cc: "H. Peter Anvin"
Cc: Ingo Molnar
Cc: Ralf Baechle
Signed-off-by: Russell King