hyperv: reduce size of ms_hyperv_info

Use the hole prior shared_gpa_boundary to store the result of get_vtl.
This reduces the size by 8 bytes.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Link: https://lore.kernel.org/r/20230922192840.3886-1-olaf@aepfle.de