arm64: kernel: suspend/resume registers save/restore

Power management software requires the kernel to save and restore
CPU registers while going through suspend and resume operations
triggered by kernel subsystems like CPU idle and suspend to RAM.

This patch implements code that provides save and restore mechanism
for the arm v8 implementation. Memory for the context is passed as
parameter to both cpu_do_suspend and cpu_do_resume functions, and allows
the callers to implement context allocation as they deem fit.

The registers that are saved and restored correspond to the registers set
actually required by the kernel to be up and running which represents a
subset of v8 ISA.

Change-Id: Ic8fcd079eee9d08a3986af363c5655785f4a4366
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Git-commit: 6732bc65c277b697f6d8b645b15f63d1558c0cc4
Git-Repo: git://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/


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