target/riscv: gdb: support vector registers for rv64 & rv32

target/riscv: gdb: support vector registers for rv64 & rv32

Signed-off-by: Hsiangkai Wang <kai.wang@sifive.com>
Signed-off-by: Greentime Hu <greentime.hu@sifive.com>
Signed-off-by: Frank Chang <frank.chang@sifive.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20211210075704.23951-69-frank.chang@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>