xf86-video-nvidia: fix acpi support

This patch fixes ACPI support in Nvidia driver on 3.14 kernel.
Without this patch I am not able to initiate Nvidia GPU on Optimus based machine.

Explanation
linux/acpi.h defines ACPI_HANDLE macro which is used in Nvidia sources
linux/acpi.h include was removed from acpi/acpi_drivers.h in 3.14

Related topics
https://devtalk.nvidia.com/default/topic/699422/nvidia-linux-334-21-drivers/?offset=4
https://devtalk.nvidia.com/default/topic/683534/331-38-on-3-14-rc1-kernel/?offset=5