arm64: Take into account ID_AA64PFR0_EL1.CSV3

arm64: Take into account ID_AA64PFR0_EL1.CSV3

BugLink: http://bugs.launchpad.net/bugs/1751064
Commit 179a56f6f9fb upstream.

For non-KASLR kernels where the KPTI behaviour has not been overridden
on the command line we can use ID_AA64PFR0_EL1.CSV3 to determine whether
or not we should unmap the kernel whilst running at EL0.

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Conflicts:
	arch/arm64/kernel/cpufeature.c
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>