it's fantastic to see this effort, and i wish you every success. i must warn you however that if you intend to use an attribution-based license, these are completely incompatible with the GPL and the LGPL, due to the attribution being "advertising". forcing people to "advertise" is an "obligation" which falls foul of the clauses which force people wishing to combine the two codebases to cease and desist from using the GPL/LGPL'd code because they cannot fulfil the requirements of the GPL/LGPL... thus completely defeating the object of combining the two codebases.
bottom line: if you insist on releasing under and attribution-based license, you will *not* see anyone using this GPU with OpenRisc or OpenSparc. both are released under the LGPL.
please consider taking some advice from people who know about software libre licenses before proceeding further with this decision. at the very least i strongly recommend to you to release the code under the LGPLv2+ because it creates a stand-alone product that requires modifications to be made publicly available under the same license. LGPLv2+ code can be used with absolutely anything.
also, from experience, i strongly recommend that you obtain a Copyright Registration Certificate for the product in the United States. this can be obtained from any Town Hall in any city in the USA. even if you are not based in the USA i strongly recommend that you consider obtaining a Copyright Registration Certificate.