[ARM] realview: fix broadcast tick support

Having discussed broadcast tick support with Thomas Glexiner, the
broadcast tick devices should be registered with a higher rating
than the global tick device, and it should have the ONESHOT and
PERIODIC feature flags set.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Thomas Glexiner <tglx@linutronix.de>