_OSI handling code grows giant and it's time to move them into one file.

This patch collects all _OSI handling code into one single file.
So that we only have the following functions to be used externally:

 early_acpi_osi_init(): Used by DMI detections;
 acpi_osi_init(): Used to initialize OSI command line settings and install
                  Linux specific _OSI handler;
 acpi_osi_setup(): The API that should be used by the external quirks.
 acpi_osi_is_win8(): The API is used by the external drivers to determine
                     if BIOS supports Win8.

CONFIG_DMI is not useful as stub dmi_check_system() can make everything
stub because of strip.

No functional changes.
Tested-by: Lukas Wunner <lukas@wunner.de>
Tested-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>