boards: st: add pllsai for ltdc input on stm32f4/stm32f7 boards

Add the pllsai configuration for boards that enables the LTDC
and are relying on the LTDC driver to perform the PLLSAI
configuration. This will allow to remove the PLLSAI code from
the LTDC driver.

Impacted boards are:
  boards/st/stm32f429i_disc1/stm32f429i_disc1.dts
  boards/st/stm32f746g_disco/stm32f746g_disco.dts
  boards/st/stm32f7508_dk/stm32f7508_dk.dts

Signed-off-by: Alain Volmat <[email protected]>

Author: Alain Volmat

boards/st/stm32f429i_disc1/stm32f429i_disc1.dts

@@ -122,6 +122,15 @@
 	status = "okay";
 };
 
+&pllsai {
+	div-m = <8>;
+	mul-n = <192>;
+	div-r = <4>;
+	div-divr = <8>;
+	clocks = <&clk_hse>;
+	status = "okay";
+};
+
 &rcc {
 	clocks = <&pll>;
 	clock-frequency = <DT_FREQ_M(168)>;

boards/st/stm32f746g_disco/stm32f746g_disco.dts

@@ -92,6 +92,15 @@
 	status = "okay";
 };
 
+&pllsai {
+	div-m = <25>;
+	mul-n = <384>;
+	div-r = <5>;
+	div-divr = <8>;
+	clocks = <&clk_hse>;
+	status = "okay";
+};
+
 &rcc {
 	clocks = <&pll>;
 	clock-frequency = <DT_FREQ_M(216)>;

boards/st/stm32f7508_dk/stm32f7508_dk.dts

@@ -83,6 +83,15 @@
 	status = "okay";
 };
 
+&pllsai {
+	div-m = <25>;
+	mul-n = <384>;
+	div-r = <5>;
+	div-divr = <8>;
+	clocks = <&clk_hse>;
+	status = "okay";
+};
+
 &rcc {
 	clocks = <&pll>;
 	clock-frequency = <DT_FREQ_M(216)>;