arm64: Implement branch predictor hardening for affected Cortex-A CPUs

arm64: Implement branch predictor hardening for affected Cortex-A CPUs

commit aa6acde65e03 upstream.

Cortex-A57, A72, A73 and A75 are susceptible to branch predictor aliasing
and can theoretically be attacked by malicious code.

This patch implements a PSCI-based mitigation for these CPUs when available.
The call into firmware will invalidate the branch predictor state, preventing
any malicious entries from affecting other victim contexts.

Co-developed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Alex Shi <alex.shi@linaro.org>
Conflicts:
	no falkor in arch/arm64/kernel/cpu_errata.c