RISC-V: KVM: Extend ONE_REG to enable/disable multiple ISA extensions

Currently, the ISA extension ONE_REG interface only allows enabling or
disabling one extension at a time. To improve this, we extend the ISA
extension ONE_REG interface (similar to SBI extension ONE_REG interface)
so that KVM user space can enable/disable multiple extensions in one
ioctl.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Anup Patel <anup@brainfault.org>