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/dts/Makefile b/arch/arm/dts/Makefile
index 15a56eb..f73ab17 100644
--- a/arch/arm/dts/Makefile
+++ b/arch/arm/dts/Makefile
@@ -1182,6 +1182,8 @@
 
 dtb-$(CONFIG_BCM47622) += \
 	bcm947622.dtb
+dtb-$(CONFIG_BCM4912) += \
+	bcm94912.dtb
 dtb-$(CONFIG_BCM63138) += \
 	bcm963138.dtb
 dtb-$(CONFIG_BCM63146) += \