drm/i915/dsi: refine send MIPI DCS command sequence

According to chapter "Sending Commands to the Panel" in bspec #29738
and #49188. If driver try to send DCS long pakcet, we have to program
TX payload register at first. And configure TX header HW register later.
DSC long packet would not be sent properly if we don't follow this
sequence.

Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
Cc: Cooper Chiou <cooper.chiou@intel.com>
Cc: William Tseng <william.tseng@intel.com>
Signed-off-by: Lee Shawn C <shawn.c.lee@intel.com>
Reviewed-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Signed-off-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210908115607.9633-3-shawn.c.lee@intel.com

drivers/gpu/drm/i915/display/icl_dsi.c

@@ -1831,11 +1831,6 @@ static ssize_t gen11_dsi_host_transfer(struct mipi_dsi_host *host,
 	if (msg->flags & MIPI_DSI_MSG_USE_LPM)
 		enable_lpdt = true;
 
-	/* send packet header */
-	ret  = dsi_send_pkt_hdr(intel_dsi_host, dsi_pkt, enable_lpdt);
-	if (ret < 0)
-		return ret;
-
 	/* only long packet contains payload */
 	if (mipi_dsi_packet_format_is_long(msg->type)) {
 		ret = dsi_send_pkt_payld(intel_dsi_host, dsi_pkt);
@@ -1843,6 +1838,11 @@ static ssize_t gen11_dsi_host_transfer(struct mipi_dsi_host *host,
 			return ret;
 	}
 
+	/* send packet header */
+	ret  = dsi_send_pkt_hdr(intel_dsi_host, dsi_pkt, enable_lpdt);
+	if (ret < 0)
+		return ret;
+
 	//TODO: add payload receive code if needed
 
 	ret = sizeof(dsi_pkt.header) + dsi_pkt.payload_length;