Revenue wise, I belive its around ~12% of their total.
How much does it make up in actual profits (%wise)? no idea...its probably profitable but not where nvidia procket much of their total profits from.
source:
http://www.tcmagazine.com/tcm/news/...million-revenue-record-tegra-sales-q1-fy-2012
AMD seems to be doing pretty good with the mobil space, with laptops ect.
Where AMD is getting a serious arse-kicking is in the Workstation GPU space.
Nvidia has lot more professional market share than AMD.
I think thats one of the reasons amd is moveing away from its "4 way VLIW SIMD" build to something new, more akin to Nvidia's fermi. I think AMD is hopeing to take some Marketshare from Nvidia's Professional line of GPU sales.