target/arm: Implement SME LD1, ST1

We cannot reuse the SVE functions for LD[1-4] and ST[1-4],
because those functions accept only a Zreg register number.
For SME, we want to pass a pointer into ZA storage.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220708151540.18136-21-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>