virt: acrn: Mark the uuid field as unused

After the commits for userspace (see Link tags below) the uuid field
is not being used in the ACRN code. Update kernel to reflect these
changes, i.e. do the following:
- adding a comment explaining that it's not used anymore
- replacing the specific type by a raw buffer
- updating the example code accordingly

The advertised field confused users and actually never been used.
So the wrong part here is that kernel puts something which userspace
never used and hence this may confuse a reader of this code.

Note, that there is only a single tool that had been prepared a year
ago for these forthcoming changes in the kernel.

Link: https://github.com/projectacrn/acrn-hypervisor/commit/da0d24326ed6
Link: https://github.com/projectacrn/acrn-hypervisor/commit/bb0327e70097
Signed-off-by: Andy Shevchenko <[e-mail]>
Acked-by: Rafael J. Wysocki <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

include/uapi/linux/acrn.h

···
 #define _UAPI_ACRN_H
 
 #include <linux/types.h>
-#include <linux/uuid.h>
 
 #define ACRN_IO_REQUEST_MAX		16
 
···
  * @reserved0:		Reserved and must be 0
  * @vcpu_num:		Number of vCPU in the VM. Return from hypervisor.
  * @reserved1:		Reserved and must be 0
- * @uuid:		UUID of the VM. Pass to hypervisor directly.
+ * @uuid:		Empty space never to be used again (used to be UUID of the VM)
  * @vm_flag:		Flag of the VM creating. Pass to hypervisor directly.
  * @ioreq_buf:		Service VM GPA of I/O request buffer. Pass to
  *			hypervisor directly.
···
 	__u16	reserved0;
 	__u16	vcpu_num;
 	__u16	reserved1;
-	guid_t	uuid;
+	__u8	uuid[16];
 	__u64	vm_flag;
 	__u64	ioreq_buf;
 	__u64	cpu_affinity;

samples/acrn/vm-sample.c

···
 
 __u16 vcpu_num;
 __u16 vmid;
-/* POST_STANDARD_VM_UUID1, refer to https://github.com/projectacrn/acrn-hypervisor/blob/master/hypervisor/include/common/vm_uuids.h */
-guid_t vm_uuid = GUID_INIT(0x385479d2, 0xd625, 0xe811, 0x86, 0x4e, 0xcb, 0x7a, 0x18, 0xb3, 0x46, 0x43);
 
 int hsm_fd;
 int is_running = 1;
···
 	}
 	hsm_fd = open("/dev/acrn_hsm", O_RDWR|O_CLOEXEC);
 
-	memcpy(&create_vm.uuid, &vm_uuid, 16);
 	create_vm.ioreq_buf = (__u64)io_req_buf;
 	ret = ioctl(hsm_fd, ACRN_IOCTL_CREATE_VM, &create_vm);
 	printf("Created VM! [%d]\n", ret);