ARM: stm32: Implement board coding on AV96

The AV96 board does exist in multiple variants. To cater for all of
them, implement board code handling. There are two GPIOs which code
the type of the board, read them out and use the value to pick the
correct device tree from an fitImage.

Reviewed-by: Patrick Delaunay <patrick.delaunay@st.com>
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc: Patrick Delaunay <patrick.delaunay@st.com>
Cc: Patrice Chotard <patrice.chotard@st.com>
Change-Id: Iddb330b9a66500495885457cbe17edc0eacaaf43
diff --git a/arch/arm/dts/stm32mp15xx-dhcom-u-boot.dtsi b/arch/arm/dts/stm32mp15xx-dhcom-u-boot.dtsi
index b57f3d5..54f7ec5 100644
--- a/arch/arm/dts/stm32mp15xx-dhcom-u-boot.dtsi
+++ b/arch/arm/dts/stm32mp15xx-dhcom-u-boot.dtsi
@@ -23,6 +23,7 @@
 		u-boot,error-led = "error";
 		st,fastboot-gpios = <&gpioa 13 GPIO_ACTIVE_LOW>;
 		st,stm32prog-gpios = <&gpioa 14 GPIO_ACTIVE_LOW>;
+		dh,som-coding-gpios = <&gpiof 12 0>, <&gpiof 13 0>, <&gpiof 15 0>;
 	};
 
 	led {