arm: bcmbca: add bcm63146 SoC support

arm: bcmbca: add bcm63146 SoC support

BCM63146 is a Broadcom B53 based DSL 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.

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: Florian Fainelli <f.fainelli@gmail.com>