arm: bcmbca: add bcm6878 SoC support

BCM6878 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 ARM PL011
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/MAINTAINERS b/MAINTAINERS
index c3a8a9d..74a240b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -220,6 +220,7 @@
 N:	bcm[9]?47622
 N:	bcm[9]?63178
 N:	bcm[9]?6846
+N:	bcm[9]?6878
 
 ARM BROADCOM BCMSTB
 M:	Thomas Fitzsimmons <fitzsim@fitzsim.org>