[intelxl] Negotiate API version for virtual function via admin queue

[intelxl] Negotiate API version for virtual function via admin queue

Do not attempt to use the admin commands to get the firmware version
and report the driver version for the virtual function driver, since
these will be rejected by the E810 firmware as invalid commands when
issued by a virtual function.  Instead, use the mailbox interface to
negotiate the API version with the physical function driver.

Signed-off-by: Michael Brown <mcb30@ipxe.org>