anv/pipeline: Pull most of the anv_pipeline_compile_* into common code

anv/pipeline: Pull most of the anv_pipeline_compile_* into common code

This leaves us with a series of little anv_pipeline_compile_* functions
which each take a compiler object, a mem_ctx, the stage to compile, and
the previous stage for VUE linking purposes.  Some of them do
interesting things but most are little more than wrappers around
brw_compile_*.

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>