gufi: prepare to move to fixed ACPI/DT kernel

Next commit will be merged soon to leg-kernel:
http://git.linaro.org/arm/acpi/acpi.git/commitdiff/13001a2d28f12fd4db80dea004b0a6a89f8bd0fa

So we will not have possibility to have both ACPI and FDT simultaneously.
This patch removes all GUFI_*_FIRST options.

Signed-off-by: Semen Protsenko <semen.protsenko@linaro.org>
gufi: choose which mechanism to use dynamically

Choose what to use (FDT or ACPI) dynamically.
This way FDT/ACPI can be choosen in bootloader (using "acpi=" kernel
parameter) and we can have single kernel image for both cases.

Signed-off-by: Semen Protsenko <semen.protsenko@linaro.org>