ARM: BCM63XX: add basic support for the Broadcom BCM63138 DSL SoC

This patch adds basic support for the Broadcom BCM63138 DSL SoC which is
using a dual-core Cortex A9 system. Add the very minimum required code
boot Linux on this SoC.

Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>