drm/dp: Add macro to check max_downspread capability

Add a macro to check for the max_downspread capability in
drm_dp_helper.

Signed-off-by: Sankeerth Billakanti <quic_sbillaka@quicinc.com>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>

changes in v4:
    - Return 1 for DPCD version >= v1.1 (Stephen Boyd)
Link: https://lore.kernel.org/r/1635839325-401-4-git-send-email-quic_sbillaka@quicinc.com

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>

include/drm/drm_dp_helper.h

@@ -1766,6 +1766,13 @@ drm_dp_tps3_supported(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
 		dpcd[DP_MAX_LANE_COUNT] & DP_TPS3_SUPPORTED;
 }
 
+static inline bool
+drm_dp_max_downspread(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
+{
+	return dpcd[DP_DPCD_REV] >= 0x11 ||
+		dpcd[DP_MAX_DOWNSPREAD] & DP_MAX_DOWNSPREAD_0_5;
+}
+
 static inline bool
 drm_dp_tps4_supported(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
 {