[S390] Use CONFIG_GENERIC_TIME and define TOD clock source.

Fix too slow clock by using CONFIG_GENERIC_TIME and adding a
clock source for the s390 time-of-day clock. As added benefit
we get rid of the s390 specific definition of do_gettimeofday
and do_settimeofday.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 51c2dfe..608193c 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -30,6 +30,9 @@
 	bool
 	default y
 
+config GENERIC_TIME
+	def_bool y
+
 config GENERIC_BUST_SPINLOCK
 	bool