target/arm: Add BFMIN, BFMAX (predicated)

target/arm: Add BFMIN, BFMAX (predicated)

FEAT_SVE_B16B16 adds bfloat16 versions of the SVE floating point
(predicated) instructions, which are encoded via sz=0b00.  Add the
BFMAX and BFMIN insns.  These have separate behaviour for AH=1 and
AH=0; we have already implemented the AH=1 helper for the SME2
versions of these insns.

Fixes: 7b1613a1020d2942 ("target/arm: Enable FEAT_SME2p1 on -cpu max")
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20250718173032.2498900-4-peter.maydell@linaro.org