arm: bcmbca: add bcm6856 SoC support under CONFIG_ARCH_BCMBCA

BCM6856 is a Broadcom B53 based PON Gateway SoC. It is part of the BCA
(Broadband Carrier Access origin) chipset family. Like other Broadband
SoC, this patch adds it under CONFIG_BCM6856 chip config and
CONFIG_ARCH_BCMBCA platform config.

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.

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: Philippe Reynes <philippe.reynes@softathome.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index 9093b98..8064e9b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -229,6 +229,7 @@
 N:	bcm[9]?6756
 N:	bcm[9]?6813
 N:	bcm[9]?6846
+N:	bcm[9]?6856
 N:	bcm[9]?6878
 
 ARM BROADCOM BCMSTB