arm64: Fix duplicated Kconfig entries

Probably due to rebasing over the lengthy time it took to get the patch
merged commit addea9ef (cpufreq: enable ARM drivers on arm64) added
a duplicate Power management options section.  Add CPUfreq to the CPU
power management section and remove a duplicate include of the main
power section.

Signed-off-by: Mark Brown <broonie@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>