drm/i915: Add early BXT sdv to the list of preproduction machines

drm/i915: Add early BXT sdv to the list of preproduction machines

Extend intel_detect_preproduction_hw() to include BXT A and B steppings.

Signed-off-by: Chris Wilson <[email protected]>
Cc: "Zanoni, Paulo R" <[email protected]>
Cc: Rodrigo Vivi <[email protected]>
Cc: Jani Nikula <[email protected]>
Cc: Ville Syrjälä <[email protected]>
Cc: Matt Roper <[email protected]>
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]
Acked-by: Jani Nikula <[email protected]>
Reviewed-by: Joonas Lahtinen <[email protected]>