RISC-V: KVM: Implement device interface for AIA irqchip

We implement KVM device interface for in-kernel AIA irqchip so that
user-space can use KVM device ioctls to create, configure, and destroy
in-kernel AIA irqchip.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Signed-off-by: Anup Patel <anup@brainfault.org>