i965: Split out per-stage dirty-bit checking into separate functions

i965: Split out per-stage dirty-bit checking into separate functions

The dirty-bit checking from each brw_upload_<stage>_prog function is
split out into its a new brw_<stage>_state_dirty function.

This commit is intended to have no functional change. It exists in
preparation for some upcoming code movement in preparation for the
shader cache.

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