[ARM] 4694/1: IXP4xx: Update clockevent support for shutdown and resume

Add proper support for CLOCK_EVT_MODE_RESUME and in the process fix
CLOCK_EVT_MODE_SHUTDOWN so that only the enable bits are toggled for both.

Signed-off-by: Kevin Hilman <khilman@mvista.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>