arm: Fix build error "conflicting types for 'scale_cpu_capacity'"

Commit "arm: Update arch_scale_cpu_capacity() to reflect change to
define" introduced a dependency on struct sched_domain in
arch/arm/include/asm/topologoy.h, but that structure is only currently
defined if CONFIG_CPU_FREQ is enabled, which causes
include/linux/cpufreq.h to get pulled in which defines it.

Include <linux/cpufreq.h> regardless of CONFIG_CPU_FREQ so struct
sched_domain is always defined.

Fixes: Change-Id: I372bd5e4c1e203428d72b18c8a806b06f3567ef6
       ("arm: Update arch_scale_cpu_capacity() to reflect change to define")
Signed-off-by: Steve Muckle <smuckle@linaro.org>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>