target/arm: Implement MVE VQSHL (vector)

target/arm: Implement MVE VQSHL (vector)

Implement the MVE VQSHL insn (encoding T4, which is the
vector-shift-by-vector version).

The DO_SQSHL_OP and DO_UQSHL_OP macros here are derived from
the neon_helper.c code for qshl_u{8,16,32} and qshl_s{8,16,32}.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210617121628.20116-33-peter.maydell@linaro.org