lib: sbi_illegal_insn: Fix FENCE.TSO emulation infinite trap loop

In case of missing "FENCE.TSO" instruction implementation,
opensbi can emulate the "FENCE.TSO" with "FENCE RW,RW", but
mepc was not incremented to continue from the next instruction
causing infinite trap.

Fixes: cb8271c ("lib: sbi_illegal_insn: Add emulation for fence.tso")
Signed-off-by: Rahul Pathak <rpathak@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Xiang W <wxjstz@126.com>
Reviewed-by: Samuel Holland <samuel@sholland.org>

lib/sbi/sbi_illegal_insn.c

@@ -40,6 +40,7 @@ static int misc_mem_opcode_insn(ulong insn, struct sbi_trap_regs *regs)
 	/* Errata workaround: emulate `fence.tso` as `fence rw, rw`. */
 	if ((insn & INSN_MASK_FENCE_TSO) == INSN_MATCH_FENCE_TSO) {
 		smp_mb();
+		regs->mepc += 4;
 		return 0;
 	}