drm/i915/bxt: Increase DDI buf idle timeout

For BXT, DDI buf idle timeout delay needs to be increased to 16us.

Since this is a timeout value and we return as soon as the condition is
realized, no penalty incurred for other platforms.

v2:
- remove TIMEOUT macro used only at a single place (Daniel)

Suggested-by: Satheeshakrishna M <satheeshakrishna.m@intel.com>
Cc: Satheeshakrishna M <satheeshakrishna.m@intel.com>
Cc: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Vandana Kannan <vandana.kannan@intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com> (v1)
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_ddi.c

@@ -322,7 +322,7 @@ static void intel_wait_ddi_buf_idle(struct drm_i915_private *dev_priv,
 	uint32_t reg = DDI_BUF_CTL(port);
 	int i;
 
-	for (i = 0; i < 8; i++) {
+	for (i = 0; i < 16; i++) {
 		udelay(1);
 		if (I915_READ(reg) & DDI_BUF_IS_IDLE)
 			return;