There is a beta bios for the board that was stated few months ago to support Bulldozer generically speaking.
Then Gigabyte deleted that info ,to stimulate new board buying i suppose , as other manufacturers made FX CPU-s to work on 890GX chipset.
Also the beta BIOS Bulldozer compatibility is something that i never seem proved yet ,thats why i have bought a 970A-UD3 few months ago .
You should contact Gigabyte support and see what beta BIOS they have in work and eventually feedback to the forum about the info.
Now if your CPU is Phenom 2 X4 965 BE you should upgrade only if you want less heat or less power consumption as the gaming performance may be similar from the FX 4170.
If you want full Bulldozer performance go for the FX 8150 the top CPU or for the FX 8120.
This CPU-s seem to also need DDR 3 1866 Mhz to show their capabilities.
Another choice would be a PII X6 CPU if you require more CPU power ,like X6 1090T or X6 1100T.
Keep in mind you may need a new motherboard if you upgrade the CPU to Bulldozer.
Why do you think you need a CPU upgrade ?!