xtensa: ccount based clockevent implementation

Reused some code from a preliminary implementation by Max Fillippov.

Cc: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Chris Zankel <chris@zankel.net>
diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index 0a1b95f..dadcf82 100644
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -6,6 +6,7 @@
 	select ARCH_WANT_FRAME_POINTERS
 	select HAVE_IDE
 	select GENERIC_ATOMIC64
+	select GENERIC_CLOCKEVENTS
 	select HAVE_GENERIC_HARDIRQS
 	select VIRT_TO_BUS
 	select GENERIC_IRQ_SHOW