arm64, dts: add hikey cpu capacity-dmips-mhz information

Hikey is an SMP platform, so this property would normally not be necessary.

But since we drive the setting of the EAS specific sched domain flag
SD_SHARE_CAP_STATES via the init_cpu_capacity_callback() cpufreq notifier
we have to make sure that cap_parsing_failed is not set to true in
parse_cpu_capacity() so that init_cpu_capacity_callback() will bail out
before consuming the CPUFREQ_NOTIFY. The easiest way to achieve this is to
provide the dts file with this property.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>