In the 7 Series FPGAs GTX/GTH Transceivers User Guide v1.4 (UG476), there is a power sequencing requirement between MGTAVTT and MGTVCCAUX mentioned in Table 5-5, page 262: "MGTAVTT must be present when power is applied to MGTVCCAUX."
This was only needed for Initial Engineering Sample (IES) silicon for the GTX; there is no longer a power sequence requirement between MGTAVTT and MGTVCCAUX. This has been corrected in v1.5 of the user guide.