ARM: dts: stm32: convert stm23f7 boards to OF_UPSTREAM

Enable OF_UPSTREAM flag for STM32F7 platforms.

Use upstream device tree for DSI and LTDC nodes,
As now in upstream DT, in panel@0 node, power-supply property is
present, which is a fixed-regulator, add DM_REGULATOR_FIXED flag
for stm32f769-disco boards.

Set also DEFAULT_FDT_FILE in defconfigs and use it in stm32f746-disco.h
to indicate which FDT file to load (All STM32F7 boards are using this
file).

If something is missing, it must be added in upstream device tree
in linux kernel ("px_clk" for DSI by example).

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
diff --git a/arch/arm/dts/stm32f746-disco-u-boot.dtsi b/arch/arm/dts/stm32f746-disco-u-boot.dtsi
index 38d797e..8ea4ea6 100644
--- a/arch/arm/dts/stm32f746-disco-u-boot.dtsi
+++ b/arch/arm/dts/stm32f746-disco-u-boot.dtsi
@@ -24,11 +24,6 @@
 	};
 };
 
-&ltdc {
-	clocks = <&rcc 0 STM32F7_APB2_CLOCK(LTDC)>;
-	bootph-all;
-};
-
 &fmc {
 	/* Memory configuration from sdram datasheet MT48LC_4M32_B2B5-6A */
 	bank1: bank@0 {
@@ -53,8 +48,14 @@
 	};
 };
 
+&ltdc {
+	bootph-all;
+
+	clocks = <&rcc 0 STM32F7_APB2_CLOCK(LTDC)>;
+};
+
 &panel_rgb {
-	compatible = "simple-panel";
+	compatible = "rocktech,rk043fn48h", "simple-panel";
 
 	display-timings {
 		timing@0 {