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/arch/arm/mach-bcmbca/Makefile b/arch/arm/mach-bcmbca/Makefile
index 3087304..87710c6 100644
--- a/arch/arm/mach-bcmbca/Makefile
+++ b/arch/arm/mach-bcmbca/Makefile
@@ -6,3 +6,4 @@
 obj-$(CONFIG_BCM47622) += bcm47622/
 obj-$(CONFIG_BCM63178) += bcm63178/
 obj-$(CONFIG_BCM6846) += bcm6846/
+obj-$(CONFIG_BCM6878) += bcm6878/