target/arm: Add BFMUL (indexed)

target/arm: Add BFMUL (indexed)

FEAT_SVE_B16B16 adds a bfloat16 version of the FMUL insn in the
floating-point multiply (indexed) instruction group. The encoding
is slightly bespoke; in our implementation we use MO_8 to indicate
bfloat16, as with the other B16B16 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: 20250718173032.2498900-5-peter.maydell@linaro.org