draw: Only run prepare when state, prim and opt changes

draw: Only run prepare when state, prim and opt changes

In bad applications like ipers which does a lot of draw calls with
no state changes this helps to greatly reduce time spent in prepare.
In ipers around 7% of CPU was spent in various prepare functions,
after this commit no prepare function show on the profile.

This commit also has the added benefit of now grouping all pipelined
drawing into a single draw call if the driver uses vbuf_render.

Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
Tested-by: Stéphane Marchesin <marcheu@chromium.org>