target/arm: Convert VFM[AS]L (scalar) to decodetree

target/arm: Convert VFM[AS]L (scalar) to decodetree

Convert the VFM[AS]L (scalar) insns in the 2reg-scalar-ext group
to decodetree. These are the last ones in the group so we can remove
all the legacy decode for the group.

Note that in disas_thumb2_insn() the parts of this encoding space
where the decodetree decoder returns false will correctly be directed
to illegal_op by the "(insn & (1 << 28))" check so they won't fall
into disas_coproc_insn() by mistake.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20200430181003.21682-11-peter.maydell@linaro.org