target/arm: Implement MVE integer min/max across vector

target/arm: Implement MVE integer min/max across vector

Implement the MVE integer min/max across vector insns
VMAXV, VMINV, VMAXAV and VMINAV, which find the maximum
from the vector elements and a general purpose register,
and store the maximum back into the general purpose
register.

These insns overlap with VRMLALDAVH (they use what would
be RdaHi=0b110).

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