target/riscv: rvv-1.0: Add Zve64f support for narrowing type-convert insns

target/riscv: rvv-1.0: Add Zve64f support for narrowing type-convert insns

Vector narrowing conversion instructions are provided to and from all
supported integer EEWs for Zve64f extension.

Signed-off-by: Frank Chang <frank.chang@sifive.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20220118014522.13613-10-frank.chang@sifive.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>