Linux-arm64 require that CNTVOFF_EL2 should be programmed with
a consistent value on all cpus. Initializing CNTVOFF_EL2 at state
transition instead of start.S could prevent potential different value
on cpus if ATF exist and u-boot runs at only one cpu.
Signed-off-by: NDavid Feng <fenghua@phytium.com.cn>