target/arm: Implement SVE2 XAR

In addition, use the same vector generator interface for AdvSIMD.
This fixes a bug in which the AdvSIMD insn failed to clear the
high bits of the SVE register.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210525010358.152808-44-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
8 files changed