target/riscv: Remove privileged spec version restriction for RVV

target/riscv: Remove privileged spec version restriction for RVV

The RVV specification does not require that the core needs to support
the privileged specification v1.12.0 to support RVV, and there is no
dependency from ISA level.

This commit removes the restriction from both RVV CSRs and extension CPU
ISA string.

Signed-off-by: Frank Chang <frank.chang@sifive.com>
Reviewed-by: Bin Meng <bmeng@tinylab.org>
Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20230208063209.27279-1-frank.chang@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>