target/riscv: fix csr check for cycle{h}, instret{h}, time{h}, hpmcounter3-31{h}

- modify check for mcounteren to work in all less-privilege mode
- modify check for scounteren to work only when S mode is enabled
- distinguish the exception type raised by check for scounteren between U
and VU mode

Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20220817083756.12471-1-liweiwei@iscas.ac.cn>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>