If CTR_EL0.{CWG,ERG} are 0b0000 then they must be interpreted to have
their architecturally maximum values, which defeats the use of
FTR_HIGHER_SAFE when sanitising CPU ID registers on heterogeneous
machines.

Introduce FTR_HIGHER_OR_ZERO_SAFE so that these fields effectively
saturate at zero.

Fixes: 3c739b57 ("arm64: Keep track of CPU feature registers")
Cc: <stable@vger.kernel.org> # 4.4.x-
Reviewed-by: NSuzuki K Poulose <suzuki.poulose@arm.com>
Acked-by: NMark Rutland <mark.rutland@arm.com>
Signed-off-by: NWill Deacon <will@kernel.org>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>