drm/panel-simple: Add 50 Hz mode to the Frida FRD350H54004 panel

By changing the pixel clock and the length of the back porch, it is
possible to obtain a perfect 50 Hz refresh rate.

v2: Rebase on drm-misc-next
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200716125647.10964-2-paul@crapouillou.net

drivers/gpu/drm/panel/panel-simple.c

@@ -1753,22 +1753,36 @@ static const struct panel_desc foxlink_fl500wvr00_a0t = {
 	.bus_format = MEDIA_BUS_FMT_RGB888_1X24,
 };
 
-static const struct drm_display_mode frida_frd350h54004_mode = {
-	.clock = 6000,
-	.hdisplay = 320,
-	.hsync_start = 320 + 44,
-	.hsync_end = 320 + 44 + 16,
-	.htotal = 320 + 44 + 16 + 20,
-	.vdisplay = 240,
-	.vsync_start = 240 + 2,
-	.vsync_end = 240 + 2 + 6,
-	.vtotal = 240 + 2 + 6 + 2,
-	.flags = DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC,
+static const struct drm_display_mode frida_frd350h54004_modes[] = {
+	{ /* 60 Hz */
+		.clock = 6000,
+		.hdisplay = 320,
+		.hsync_start = 320 + 44,
+		.hsync_end = 320 + 44 + 16,
+		.htotal = 320 + 44 + 16 + 20,
+		.vdisplay = 240,
+		.vsync_start = 240 + 2,
+		.vsync_end = 240 + 2 + 6,
+		.vtotal = 240 + 2 + 6 + 2,
+		.flags = DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC,
+	},
+	{ /* 50 Hz */
+		.clock = 5400,
+		.hdisplay = 320,
+		.hsync_start = 320 + 56,
+		.hsync_end = 320 + 56 + 16,
+		.htotal = 320 + 56 + 16 + 40,
+		.vdisplay = 240,
+		.vsync_start = 240 + 2,
+		.vsync_end = 240 + 2 + 6,
+		.vtotal = 240 + 2 + 6 + 2,
+		.flags = DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC,
+	},
 };
 
 static const struct panel_desc frida_frd350h54004 = {
-	.modes = &frida_frd350h54004_mode,
-	.num_modes = 1,
+	.modes = frida_frd350h54004_modes,
+	.num_modes = ARRAY_SIZE(frida_frd350h54004_modes),
 	.bpc = 8,
 	.size = {
 		.width = 77,