Disable Turbo on steppings prior to B0 on BXT due to hangs seen during GT CPD exit.

Change-Id: I50c5c03f59f5ba092db19e17234951d89db42c6c
Signed-off-by: Sagar Arun Kamble <sagar.a.kamble@intel.com>
Reviewed by: Alex Dai <yu.dai@intel.com>.
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>