arm: bcmbca: add bcm6846 SoC support

BCM6846 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 Broadcom 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/board/broadcom/bcmbca/Kconfig b/board/broadcom/bcmbca/Kconfig
index 5384676..70ca380 100644
--- a/board/broadcom/bcmbca/Kconfig
+++ b/board/broadcom/bcmbca/Kconfig
@@ -22,3 +22,10 @@
 	default "bcm963178"
 
 endif
+
+if TARGET_BCM96846
+
+config SYS_CONFIG_NAME
+	default "bcm96846"
+
+endif