> I don't know, what "lite" version means. I only know, that
> in older Powermacs is U3 and in older iMacs U3 lite.

According to technical reports, U3 lite can interface to only one CPU where the full U3 can interface to two CPUs. Additionally, U3 lite may or may not have a lower clock rate limit compared to the full U3.

> there can but cannot be U4 lite version for newer iMacs.

In contrast to the U3 lite, I never heard or read anything of an "U4 lite", that's why I've been assuming that, opposed to the AGP G5 generation, the PCIe iMacs use a full (i.e. non-crippled) version of the U4 northbridge chip, just at a lower clock rate (maybe even underclocked for product differentiation reasons?) than on the PowerMacs and leaving one CPU interface unused.

> If this photo is Northbrige from your real iMac

This photo titled "CPC945 a.k.a. Kodiak. On iMac G5 (iSight) 17-inch 1.9 GHz" isn't my photo, just one I found through a quick search :-)

> it is possible to find according manual.

Yes, searching for the string "41E4244" from the photo above reveals the CPC945 datasheet from August 2006 (there's also a newer one from December 2007, but that should be irrelevant as the iMac G5 iSight was discontinued in January 2006). There in the "Speed Classification" column in the bottom table on page 12 you can see that the "41E4244" part comes out third fastest out of six available.
Now we'd need photos of CPC945 chips of different PCIe PowerMac models to conclude if they are from the same or faster speed classification. Maybe even the 2.1 GHz iMac G5 iSight has a faster rated part than the "41E4244" one of the 1.9 GHz model?
In any case: All listed part numbers, including the one found in the iMac G5 iSight 1.9 GHz, are full versions with two CPU interfaces, so from this I think we can assume that there exists no "U4 lite", at least not in any Mac.