i965: Skip uploading border color when unnecessary.

i965: Skip uploading border color when unnecessary.

The border color is only needed when using the GL_CLAMP_TO_BORDER or
(deprecated) GL_CLAMP wrap modes; all others ignore it, including the
common GL_CLAMP_TO_EDGE and GL_REPEAT wrap modes.

In those cases, we can skip uploading it entirely, saving a bit of space
in the batchbuffer.  Instead, we just point it at the start of the
batch (offset 0); we have to program something, and that address is safe
to read.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>