target/arm: Implement MVE integer vector-vs-scalar comparisons

target/arm: Implement MVE integer vector-vs-scalar comparisons

Implement the MVE integer vector comparison instructions that compare
each element against a scalar from a general purpose register.  These
are "VCMP (vector)" encodings T4, T5 and T6 and "VPT (vector)"
encodings T4, T5 and T6.

We have to move the decodetree pattern for VPST, because it
overlaps with VCMP T4 with size = 0b11.

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