phycore-am62x: Migrate to OF_UPSTREAM

The phycore-am62x can be migrated to OF_UPSTREAM.
Drop redundant device tree files, update MAINTAINERS and
defconfig's DEFAULT_DEVICE_TREE for ti vendor prefix accordingly.

Signed-off-by: Wadim Egorov <w.egorov@phytec.de>
diff --git a/arch/arm/dts/k3-am625-phycore-som-binman.dtsi b/arch/arm/dts/k3-am625-phycore-som-binman.dtsi
index ed50bfe..dbee4aa 100644
--- a/arch/arm/dts/k3-am625-phycore-som-binman.dtsi
+++ b/arch/arm/dts/k3-am625-phycore-som-binman.dtsi
@@ -140,7 +140,7 @@
 #endif /* CONFIG_TARGET_PHYCORE_AM62X_R5 */
 
 #ifdef CONFIG_TARGET_PHYCORE_AM62X_A53
-#define SPL_AM625_PHYBOARD_LYRA_DTB "spl/dts/k3-am625-phyboard-lyra-rdk.dtb"
+#define SPL_AM625_PHYBOARD_LYRA_DTB "spl/dts/ti/k3-am625-phyboard-lyra-rdk.dtb"
 #define AM625_PHYBOARD_LYRA_DTB "u-boot.dtb"
 
 &binman {