arm64: Add Broadcom iProc family support

This patch adds support to Broadcom's iProc family of arm64 based SoCs
in the arm64 Kconfig and defconfig files

Signed-off-by: Ray Jui <rjui@broadcom.com>
Reviewed-by: Scott Branden <sbranden@broadcom.com>
Signed-off-by: Olof Johansson <olof@lixom.net>