ARM: 7085/2: mach-integrator: clockevent supports oneshot mode

The Integrator AP timer has no problem supporting oneshot
ticks with proper code, so let's do it so we can have
NOHZ configured in for this platform too.

Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>