Hello,
The bitfile is loaded by U-boot. In principle, an environment variable needs to be modified to make it load a file with a different name. You may override the default setting and save it to the QSPI flash. This is briefly discussed in section 4.3.3 of the Getting started with Xillinux guide:
http://xillybus.com/downloads/doc/xilly ... d_zynq.pdfRegards,
Eli