drivers base/arch_topology: Remove 'struct sched_domain' forward declaration

The sched domain pointer argument from topology_get_freq_scale() and
topology_get_cpu_scale() got removed by commit 7673c8a4
("sched/cpufreq: Remove arch_scale_freq_capacity()'s 'sd' parameter")
and commit 8ec59c0f

 ("sched/topology: Remove unused 'sd' parameter
from arch_scale_cpu_capacity()").

So the 'struct sched_domain' forward declaration is no longer needed.
Remove it.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Link: https://lore.kernel.org/r/20200211181515.32570-2-dietmar.eggemann@arm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>