RISC-V: KVM: Allow bfloat16 extension for Guest/VM

RISC-V: KVM: Allow bfloat16 extension for Guest/VM

Extend the KVM ISA extension ONE_REG interface to allow KVM user space
to detect and enable Zfbfmin/Zvfbfmin/Zvfbfwma extension for Guest/VM.

Signed-off-by: Quan Zhou <zhouquan@iscas.ac.cn>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Nutty Liu <nutty.liu@hotmail.com>
Reviewed-by: Nutty Liu <liujingqi@lanxincomputing.com>
Link: https://lore.kernel.org/r/f846cecd330ab9fc88211c55bc73126f903f8713.1754646071.git.zhouquan@iscas.ac.cn
Signed-off-by: Anup Patel <anup@brainfault.org>