arm64 relies on the arm_arch_timer for sched_clock, so we can select
HAVE_IRQ_TIME_ACCOUNTING and have the core sched-clock code enable the
feature at runtime based on the rate.
Reported-by: NMario Smarduch <m.smarduch@samsung.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>