arm64/topology: link arch_scale_min_freq_capacity to cpufreq

Cpufreq tracks minimum frequency constraints per-cpu.
Link this to the generic arch_scale_min_freq_capacity which is
used in the scheduler.

Change-Id: I9f4f838bc7ebf929947ccc9e729e5ab24728e81c
Signed-off-by: Chris Redpath <chris.redpath@arm.com>
Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com>