RFC: freedreno: prepare for a3xx

Split the parts that are specific to adreno a2xx series GPUs from the
parts that will be in common with a3xx, so that a3xx support can be
added more cleanly.
RFC: freedreno: add a3xx support

The adreno a3xx GPU is found in newer snapdragon devices, such as the
nexus4.  The a3xx is GLESv3 and OpenCL capable, although that is not
enabled yet in gallium.

Compared to a2xx, it introduces an entirely new unified shader ISA, and
re-shuffles all or nearly all of the registers.  The good news is that
(for the most part) the registers are more orthogonal, not combining
unrelated state in a single register.  And that there is a lot more
flexibility, so we don't need to patch and re-emit the shader like we
did on a2xx.

The shader compiler is currently quite dumb, there would be a lot of
room for improvement with an optimizing pass.  Despite that, with the
a320 in my nexus4 it seems to be ~2-3x faster compared to the a220 in my
HP touchpad.