arm: bcmbca: add bcm6846 SoC support

BCM6846 is an ARM A7 based PON Broadband SoC. It is part of the BCA
(Broadband Carrier Access origin) chipset family so it's added under
ARCH_BCMBCA platform. This initial support includes a bare-bone
implementation and dts with CPU subsystem, memory and Broadcom uart.

This SoC is supported in the linux-next git repository so the dts and
dtsi files are copied from linux with minor fix-up that needs to be
upstreamed to linux as well.

The u-boot image can be loaded from flash or network to the entry point
address in the memory and boot from there.

Signed-off-by: William Zhang <william.zhang@broadcom.com>
diff --git a/arch/arm/dts/bcm96846.dts b/arch/arm/dts/bcm96846.dts
new file mode 100644
index 0000000..c70ebcc
--- /dev/null
+++ b/arch/arm/dts/bcm96846.dts
@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: (GPL-2.0+ OR MIT)
+/*
+ * Copyright 2022 Broadcom Ltd.
+ */
+
+/dts-v1/;
+
+#include "bcm6846.dtsi"
+
+/ {
+	model = "Broadcom BCM96846 Reference Board";
+	compatible = "brcm,bcm96846", "brcm,bcm6846", "brcm,bcmbca";
+
+	aliases {
+		serial0 = &uart0;
+	};
+
+	chosen {
+		stdout-path = "serial0:115200n8";
+	};
+
+	memory@0 {
+		device_type = "memory";
+		reg = <0x0 0x08000000>;
+	};
+};
+
+&uart0 {
+	status = "okay";
+};