drivers base/arch_topology: allow inlining cpu-invariant accounting support

Allow inlining of topology_get_cpu_scale() into the task
scheduler fast path (e.g. __update_load_avg_se()) by coding it as a
static inline function in the arch topology header file.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>