Incorrect TDL's SSP address shift in SARB for 16:6 & 18:8 modes.
Disable the Sampler state prefetch functionality in the SARB by
programming 0xB000[30] to '1'. This is to be done at boot time
and the feature must remain disabled permanently.

Fixes flaky tex-mip-level-selection* piglit tests with Mesa i965
driver.

Cc: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181004182939.7668-6-radhakrishna.sripada@intel.com