drm/i915/skl: Provide a get_aux_send_ctl() vfunc for skylake

Skylake doesn't use the pre-charge field now, but, instead, we need to
specify the total number of SYNC pulses for the SYNC phase (pre-charge +
SYNC pattern pules). Let's use the default value (32) for that.

v3: increase DP AUX TX timeout as 400us is not to be used on SKL
    apparently (Jesse).

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 1eaa341..d4af99e 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -3634,6 +3634,7 @@
 #define   DP_AUX_CH_CTL_PRECHARGE_TEST	    (1 << 11)
 #define   DP_AUX_CH_CTL_BIT_CLOCK_2X_MASK    (0x7ff)
 #define   DP_AUX_CH_CTL_BIT_CLOCK_2X_SHIFT   0
+#define   DP_AUX_CH_CTL_SYNC_PULSE_SKL(c)   ((c) - 1)
 
 /*
  * Computing GMCH M and N values for the Display Port link