ARM64: Remove duplicated Kconfig entry for "kernel/power/Kconfig"

There is a duplicated Kconfig entry for "kernel/power/Kconfig"
in menu "Power management options" and "CPU Power Management",
remove the one from menu "CPU Power Management" suggested by
Viresh.
Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/Kconfig

@@ -323,8 +323,6 @@ menu "CPU Power Management"
 
 source "drivers/cpuidle/Kconfig"
 
-source "kernel/power/Kconfig"
-
 source "drivers/cpufreq/Kconfig"
 
 endmenu