Group optional configurations in av1/av1.cmake.
Group optional configurations in av1/av1.cmake.

Change-Id: I0dd17ec7ea59cecf8298831d0e46e971f744c2c7

smarter/aom,GrokImageCompression/aom,luctrudeau/aom,luctrudeau/aom,GrokImageCompression/aom,luctrudeau/aom,GrokImageCompression/aom,smarter/aom,luctrudeau/aom,luctrudeau/aom,smarter/aom,smarter/aom,GrokImageCompression/aom,GrokImageCompression/aom,smarter/aom,smarter/aom,luctrudeau/aom,GrokImageCompression/aom