RISC-V: KVM: Add exit logic to main.c

Several lines of code are inserted to remove KVM module normally
using rmmod command just like others.

Signed-off-by: XiakaiPan <13212017962@163.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Tested-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Anup Patel <anup@brainfault.org>

Author: XiakaiPan

arch/riscv/kvm/main.c

@@ -127,3 +127,9 @@ static int __init riscv_kvm_init(void)
 	return kvm_init(NULL, sizeof(struct kvm_vcpu), 0, THIS_MODULE);
 }
 module_init(riscv_kvm_init);
+
+static void __exit riscv_kvm_exit(void)
+{
+	kvm_exit();
+}
+module_exit(riscv_kvm_exit);