target/riscv: Add support for Zve64x extension

target/riscv: Add support for Zve64x extension

Add support for Zve64x extension. Enabling Zve64f enables Zve64x and
enabling Zve64x enables Zve32x according to their dependency.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2107
Signed-off-by: Jason Chien <jason.chien@sifive.com>
Reviewed-by: Frank Chang <frank.chang@sifive.com>
Reviewed-by: Max Chou <max.chou@sifive.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-ID: <20240328022343.6871-3-jason.chien@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>