[PATCH 1/5] mountmgr.sys: Move query_unix_drive to drive.c.

[Erich E. Hoover]

The purpose of this patchset is to further consolidate the volume
information in the mountmgr.  Currently there are a couple of
different paths that can be taken to obtain the volume information, by
the end of this set all
FileFsAttributeInformation/FileFsVolumeInformation queries run through
the same code in the mountmgr.

This particular patch just moves query_unix_device to facilitate code
reuse in later patches.

Best,
Erich