freedreno/drm-shim: Add support for faking other adreno chips.

I wanted to look at the effect of a core NIR change on a2xx codegen, but I don't have any of those boards. This could also prove useful for quickly sanity-checking the compiler by running shader-db on it -- a2xx fails in a few ways on glmark2, and a3xx-a5xx fails on glmark2 in a debug_assert (which we don't have enabled in our dEQP runs).