drivers/firmware: Expose psci_get_version through psci_ops structure

Entry into recent versions of ARM Trusted Firmware will invalidate the CPU
branch predictor state in order to protect against aliasing attacks.

This patch exposes the PSCI "VERSION" function via psci_ops, so that it
can be invoked outside of the PSCI driver where necessary.

Change-Id: Ibe7995e9a311eb7da441d3c65dfdf71e9de3b33c
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Git-commit: d68e3ba5303f7e1099f51fdcd155f5263da8569b
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux


[neeraju@codeaurora.org: resolve merge conflicts due to
 missing files]
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>