i965: Massively simplify the intel_upload implementation.

i965: Massively simplify the intel_upload implementation.

The implementation kept a page-sized area for uploading data, and
uploaded chunks from that to a 64kb-sized streamed buffer.  This wasted
cache footprint (and extra state tracking to do so) when we want to just
write our data into the buffer immediately.

Instead, build it around an interface like brw_state_batch() that just
gets you a pointer to BO memory to upload your stuff immediately.

Improves OpenArena on HSW by 1.62209% +/- 0.355299% (n=61) and on BYT by
1.7916% +/- 0.415743% (n=31).

v2: Rebase on Mesa master, drop old prototypes.  Re-do performance
    comparison on a kernel that doesn't punish CPU efficiency
    improvements.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>