drm/i915/vlv_dsi: Double pixelclock on read-back for dual-link panels

In intel_dsi_get_config() double the pclk returned by foo_dsi_get_pclk()
for dual-link panels. This fixes the following WARN triggering:

 i915 0000:00:02.0: [drm] *ERROR* [CRTC:51:pipe A] mismatch in pixel_rate (expected 235710, found 118056)
 i915 0000:00:02.0: [drm] *ERROR* [CRTC:51:pipe A] mismatch in hw.pipe_mode.crtc_clock (expected 235710, found 118056)
 i915 0000:00:02.0: [drm] *ERROR* [CRTC:51:pipe A] mismatch in hw.adjusted_mode.crtc_clock (expected 235710, found 118056)
 i915 0000:00:02.0: [drm] *ERROR* [CRTC:51:pipe A] mismatch in port_clock (expected 235710, found 118056)
 ------------[ cut here ]------------
 pipe state doesn't match!
 WARNING: CPU: 3 PID: 136 at drivers/gpu/drm/i915/display/intel_display.c:9125 intel_display_finish_reset+0x1bd3/0x2050 [i915]
 ...

This has been tested on a Xiaomi Mi Pad 2 (with CHT x5-Z8500 SoC) tablet,
with a 1536x2048 dual-link DSI panel.

Note this fix was taken from icl_dsi.c which does the same in
its get_config().

Cc: Tsuchiya Yuto <kitakar@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211024155020.126328-1-hdegoede@redhat.com

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

@@ -1258,7 +1258,9 @@ static void intel_dsi_get_config(struct intel_encoder *encoder,
 				 struct intel_crtc_state *pipe_config)
 {
 	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
+	struct intel_dsi *intel_dsi = enc_to_intel_dsi(encoder);
 	u32 pclk;
+
 	drm_dbg_kms(&dev_priv->drm, "\n");
 
 	pipe_config->output_types |= BIT(INTEL_OUTPUT_DSI);
@@ -1270,6 +1272,9 @@ static void intel_dsi_get_config(struct intel_encoder *encoder,
 		pclk = vlv_dsi_get_pclk(encoder, pipe_config);
 	}
 
+	if (intel_dsi->dual_link)
+		pclk *= 2;
+
 	if (pclk) {
 		pipe_config->hw.adjusted_mode.crtc_clock = pclk;
 		pipe_config->port_clock = pclk;