x86: rework AMX multiplication insn disassembly

x86: rework AMX multiplication insn disassembly

Consistently do 64-bit first, ModR/M second, VEX.L third, VEX.W fourth,
and prefix last, resulting in fewer table entries. Note that in the
course of the re-work wrong M_0 suffixes are also corrected to be M_1
(partly infixes now).

Since it ended up confusing while testing the change, also adjust the
test name in x86-64-amx-bad.d (to be distinct from x86-64-amx.d's).