IN  PSUBSECTION Subsection,
  IN  PMMPTE PteAddress

Routine Description:

    This function calculates the file offset given a subsection and a PTE
    offset.  Note that images are stored in 512-byte units whereas data is
    stored in 4K units.

    When this is all debugged, this should be made into a macro.


    Subsection - Supplies a subsection to reference for the file address.

    PteAddress - Supplies a PTE within the subsection

Return Value:

    Returns the file offset to obtain the backing data from.