drm/i915/display: Take into account AS SDP in intel_dp_sdp_min_guardband

drm/i915/display: Take into account AS SDP in intel_dp_sdp_min_guardband

We started seeing "[drm] *ERROR* Timed out waiting PSR idle state" after
taking optimized guardband into use. These are seen because VSC SDPs are
sent on same line as AS SDPs when AS SDP is enabled. AS SDP is sent on line
configured in EMP_AS_SDP_TL register. We are configuring
crtc_state->vrr.vsync_start into that register.

Fix this by ensuring AS SDP is sent on line which is within
guardband. From the bspec:

EMP_AS_SDP_TL < SCL + Guardband

v2: check HAS_AS_SDP

Bspec: 71197
Fixes: 52ecd48b8d3f ("drm/i915/dp: Add helper to get min sdp guardband")
Cc: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://lore.kernel.org/r/20251023043140.961104-1-jouni.hogander@intel.com