arm64: add CPU power management menu/entries

This patch provides a menu for CPU power management options in the
arm64 Kconfig and adds an entry to enable the generic CPU idle configuration.

Change-Id: Ib914d0082b1a8c9d95faebd79a4bd0f3be2f5cbd
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Git-commit: 1307220d7bb79fc526d006f854ebfd2bf44e6e87
Git-Repo: git://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git


Signed-off-by: Abhimanyu Kapur <abhimany@codeaurora.org>