arm: dts: am335x: add 'u-boot, dm-pre-reloc' to panel

Add the "u-boot,dm-pre-reloc" property to the "ti,tilcdc,panel"
compatible node. In this way the video-uclass module can allocate the
amount of memory needed to be assigned to the frame buffer.
For boards that support Linux the property is added to the *-u-boot.dtsi
file since it is a u-boot specific dt flag.

Ran building tests with CONFIG_AM335X_LCD enabled and disabled for the
following configurations:
 - brxre1_defconfig           --> success
 - am335x_guardian_defconfig  --> success
 - am335x_evm_defconfig       --> success
 - da850evm_defconfig         --> failure with CONFIG_AM335X_LCD enabled

Enabling CONFIG_AM335X_LCD in da850evm_defconfig causes building errors
even without applying the patch. The driver has never been enabled on the
da850 and must be adapted for this platform.

Signed-off-by: Dario Binacchi <dariobin@libero.it>
Tested-by: Dario Binacchi <dariobin@libero.it>
Reviewed-by: Felix Brack <fb@ltec.ch>
diff --git a/arch/arm/dts/am335x-rut-u-boot.dtsi b/arch/arm/dts/am335x-rut-u-boot.dtsi
new file mode 100644
index 0000000..b2b4aa5
--- /dev/null
+++ b/arch/arm/dts/am335x-rut-u-boot.dtsi
@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * am335x-rut U-Boot Additions
+ *
+ * Copyright (C) 2020 Dario Binacchi <dariobin@libero.it>
+ */
+
+/ {
+	panel {
+		u-boot,dm-pre-reloc;
+	};
+};