board: ti: am65x: migrate to OF_UPSTREAM

Rather than rely on manual updates from the arch/arm/dts directory,
enable CONFIG_OF_UPSTREAM to receive automatic device tree updates for
the am65x reference board.

Signed-off-by: Bryan Brattlof <bb@ti.com>
diff --git a/arch/arm/dts/Makefile b/arch/arm/dts/Makefile
index 042282f..0c8e84a 100644
--- a/arch/arm/dts/Makefile
+++ b/arch/arm/dts/Makefile
@@ -1156,9 +1156,7 @@
 	stm32mp257f-ev1.dtb
 
 dtb-$(CONFIG_SOC_K3_AM654) += \
-	k3-am654-base-board.dtb \
-	k3-am654-r5-base-board.dtb \
-	k3-am654-icssg2.dtbo
+	k3-am654-r5-base-board.dtb
 
 dtb-$(CONFIG_SOC_K3_J721E) += k3-j721e-r5-common-proc-board.dtb \
 			      k3-j7200-r5-common-proc-board.dtb \