verdin-am62: move verdin am62 to OF_UPSTREAM

Move verdin-am62 to OF_UPSTREAM:
- handle the fact that dtbs now have a 'ti/' prefix
- imply OF_UPSTREAM
- remove redundant files from arch/arm/dts leaving only the
  *-u-boot.dtsi files
- update MAINTAINERS file

Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Reviewed-by: Dhruva Gole <d-gole@ti.com>
Reviewed-by: Neha Malcom Francis <n-francis@ti.com>
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
diff --git a/arch/arm/mach-k3/am62x/Kconfig b/arch/arm/mach-k3/am62x/Kconfig
index 7c9bac2..9786751 100644
--- a/arch/arm/mach-k3/am62x/Kconfig
+++ b/arch/arm/mach-k3/am62x/Kconfig
@@ -48,6 +48,7 @@
 	select ARM64
 	select BINMAN
 	select OF_SYSTEM_SETUP
+	imply OF_UPSTREAM
 
 config TARGET_VERDIN_AM62_R5
 	bool "Toradex Verdin AM62 running on R5"