sim/riscv: fix multiply instructions on simulator

After this commit:

  commit 0938b032da
  Date:   Wed Feb 2 10:06:15 2022 +0900

      RISC-V: Add 'Zmmul' extension in assembler.

some instructions in the RISC-V simulator stopped working as a new
instruction class 'INSN_CLASS_ZMMUL' was added, and some existing
instructions were moved into this class.

The simulator doesn't currently handle this instruction class, and so
the instructions will now cause an illegal instruction trap.

This commit adds support for INSN_CLASS_ZMMUL, and adds a test that
ensures the affected instructions can be executed by the simulator.

Reviewed-by: Palmer Dabbelt <palmer@rivosinc.com>
Reviewed-by: Andrew Burgess <aburgess@redhat.com>

sim/riscv/sim-main.c

@@ -936,6 +936,7 @@ execute_one (SIM_CPU *cpu, unsigned_word iw, const struct riscv_opcode *op)
     case INSN_CLASS_I:
       return execute_i (cpu, iw, op);
     case INSN_CLASS_M:
+    case INSN_CLASS_ZMMUL:
       return execute_m (cpu, iw, op);
     default:
       TRACE_INSN (cpu, "UNHANDLED EXTENSION: %d", op->insn_class);

sim/testsuite/riscv/m-ext.s

@@ -0,0 +1,18 @@
+# Check that the RV32M instructions run without any faults.
+# mach: riscv
+
+.include "testutils.inc"
+
+	start
+
+	.option	arch, +m
+	mul	x0, x1, x2
+	mulh	x0, x1, x2
+	mulhu	x0, x1, x2
+	mulhsu	x0, x1, x2
+	div	x0, x1, x2
+	divu	x0, x1, x2
+	rem	x0, x1, x2
+	remu	x0, x1, x2
+
+	pass