target/arm: Implement the ARMv8.1-HPD extension

target/arm: Implement the ARMv8.1-HPD extension

Since the TCR_*.HPD bits were RES0 in ARMv8.0, we can simply
interpret the bits as if ARMv8.1-HPD is present without checking.
We will need a slightly different check for hpd for aarch32.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20181203203839.757-10-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>