target/riscv: rvv: Remove the dependency of Zvfbfmin to Zfbfmin

target/riscv: rvv: Remove the dependency of Zvfbfmin to Zfbfmin

According to the Zvfbfmin definition in the RISC-V BF16 extensions spec,
the Zvfbfmin extension only requires either the V extension or the
Zve32f extension.

Signed-off-by: Max Chou <max.chou@sifive.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20240321170929.1162507-1-max.chou@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>