i965: Don't emit SURFACE_STATEs for gather workarounds on Broadwell.

i965: Don't emit SURFACE_STATEs for gather workarounds on Broadwell.

As far as I can tell, Broadwell doesn't need any of the SURFACE_STATE
workarounds for textureGather() bugs, so there's no need to emit
a second set of identical copies.

To keep things simple, just point the gather surface index base to the
same place as the texture surface index base.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>
Cc: "10.2" <mesa-stable@lists.freedesktop.org>