target/arm: Implement MVE integer vector comparisons

target/arm: Implement MVE integer vector comparisons

Implement the MVE integer vector comparison instructions.  These are
"VCMP (vector)" encodings T1, T2 and T3, and "VPT (vector)" encodings
T1, T2 and T3.

These insns compare corresponding elements in each vector, and update
the VPR.P0 predicate bits with the results of the comparison.  VPT
also sets the VPR.MASK01 and VPR.MASK23 fields -- it is effectively
"VCMP then VPST".

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