arm: bcmbca: add bcm4912 SoC support

BCM4912 is a Broadcom B53 based WLAN AP router 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 ARM PL011 uart.

This SoC is supported in the linux-next git repository so the dts
and dtsi files are copied from linux.

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

Signed-off-by: William Zhang <william.zhang@broadcom.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
diff --git a/arch/arm/mach-bcmbca/bcm4912/Kconfig b/arch/arm/mach-bcmbca/bcm4912/Kconfig
new file mode 100644
index 0000000..b8c14d1
--- /dev/null
+++ b/arch/arm/mach-bcmbca/bcm4912/Kconfig
@@ -0,0 +1,17 @@
+# SPDX-License-Identifier: GPL-2.0+
+#
+# (C) Copyright 2022 Broadcom Ltd
+#
+
+if BCM4912
+
+config TARGET_BCM94912
+	bool "Broadcom 4912 Reference Board"
+	depends on ARCH_BCMBCA
+
+config SYS_SOC
+	default "bcm4912"
+
+source "board/broadcom/bcmbca/Kconfig"
+
+endif