arm/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: I351dc1d45d8722cf1d6361ca843c6b49e9732665
Signed-off-by: Chris Redpath <chris.redpath@arm.com>
Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com>