ARM: add SCHED_HRTICK config option

As we don't include kernel/Kconfig.hz as this defines HZ values
unsuitable for ARM platforms, add the SCHED_HRTICK to properly configure
the scheduler for hrtimer operation.

Change-Id: I1dd68d4b0481bcf37e4bafd9192b29d0509db80f
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>