We currently don't log the boot mode for arm64 as we do for arm, and
without KVM the user is provided with no indication as to which mode(s)
CPUs were booted in, which can seriously hinder debugging in some cases.

Add logging to the boot path once all CPUs are up. Where CPUs are
mismatched in violation of the boot protocol, WARN and set a taint (as
we do for CPU other CPU feature mismatches) given that the
firmware/bootloader is buggy and should be fixed.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Tested-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: NMark Rutland <mark.rutland@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>