drm/i915/gt: Leave RING_BB_STATE to default value

Do not reset RING_BB_STATE, leaving it to the default state value. This
prevents bdw/bsw from getting confused when executing batches from the
GGTT.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191230165821.3840449-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/intel_lrc.c

@@ -3968,7 +3968,6 @@ static void init_common_reg_state(u32 * const regs,
 					    CTX_CTRL_RS_CTX_ENABLE);
 
 	regs[CTX_RING_CTL] = RING_CTL_SIZE(ring->size) | RING_VALID;
-	regs[CTX_BB_STATE] = RING_BB_PPGTT;
 }
 
 static void init_wa_bb_reg_state(u32 * const regs,