arm: bcmbca: add bcm6858 SoC support under CONFIG_ARCH_BCMBCA

BCM6858 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_BCM6858 chip config and
CONFIG_ARCH_BCMBCA platform config.

This initial support includes a bare-bone implementation and the
original dts is updated with the one from linux next git repository.

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 8064e9b..e86ffc0 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -230,6 +230,7 @@
 N:	bcm[9]?6813
 N:	bcm[9]?6846
 N:	bcm[9]?6856
+N:	bcm[9]?6858
 N:	bcm[9]?6878
 
 ARM BROADCOM BCMSTB