target/arm: Implement MVE VSHLC

Implement the MVE VSHLC insn, which performs a shift left of the
entire vector with carry in bits provided from a general purpose
register and carry out bits written back to that register.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210628135835.6690-14-peter.maydell@linaro.org