mesa: rename PreferDP4 to OptimizeForAOS.

This flag was really just a proxy for determining whether the backend
was vector (AOS) or scalar (SOA). It will be used to apply a future
optimization only for vector backends.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
8 files changed