ACPI: GUFI: add kernel config options for GUFI

Introduce the kernel config options to enable the Grand Unified Firmware
Interface (GUFI).  Give the user the option of using only ACPI, only DT,
or searching both with either ACPI or DT being searched first.

Signed-off-by: Al Stone <al.stone@linaro.org>
enable acpi for aarch64
initial gufi skeleton
some additional functionality, still WIP