Is it possible to combine these two architectures on software/driver level ?
Basically, could GCN 1.0 card operate within the driver like GCN 2.0 card?
Though some features may work but overall I don't think it's likely to happen due to the architectural limitations that 1st generation GCN cards have compared to 2nd generation cards.
First GCN 2.0 is a superset of capabilities beyond GCN 1.0. GCN 1.0 is also only compatible with OpenCL 1.2. GCN 2.0 is compatible with new feature specified in OpenCL 2.0 spec. So to get to answer your looking for if you develop an OpenCL 1.2 program it will run on GCN 1.0, 1.1, and 2.0 enabled GPU's. We JIT the program from OpenCL source to proper GCN machine instructions for you.
Blender no longer supports my card AMD 7870. I can't select Pitcairn OpenCL anymore due to unsolvable issues in the compiler which Blender developers have.
Is there is some solution to rewrite the drivers for 7870 so that I could be able to use it