[ARM] 3856/1: Add clocksource for Intel IXP4xx platforms

Enables the ixp4xx platforms to use Generic time-of-day.

Signed-off-by: Kevin Hilman <khilman@mvista.com>
Acked-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Deepak Saxena <dsaxena@plexity.net>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>