arm64: Broadcom Vulcan support

Add a configuration option and a device tree for Broadcom's Vulcan
ARM64 processor. vulcan.dtsi has the on-chip blocks like the PCIe
controller, GICv3 with ITS, PMU, system timer and the pl011 UART.
vulcan-eval.dts has definitions for a basic evaluation board.

Vulcan's processor cores support the ARMv8.1 instruction set and
will use "brcm,vulcan" as the compatible property. The firmware
has PSCI 0.2 support for cpu wakeup.

Signed-off-by: Zi Shen Lim <zlim@broadcom.com>
[ updated and split dts - jchandra@broadcom.com ]
Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>