target/riscv: Fix exception type when VU accesses supervisor CSRs

target/riscv: Fix exception type when VU accesses supervisor CSRs

When supervisor CSRs are accessed from VU-mode, a virtual instruction
exception should be raised instead of an illegal instruction.

Fixes: c1fbcecb3a (target/riscv: Fix csr number based privilege checking)
Signed-off-by: Xu Lu <luxu.kernel@bytedance.com>
Reviewed-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Nutty Liu <liujingqi@lanxincomputing.com>
Message-ID: <20250708060720.7030-1-luxu.kernel@bytedance.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>