Normally, if a device uses larger physical sector size than the logical
size and supports so-called "512e" mode, we let the device deal with
partial sector reads/writes.
However, if MAX_VIRT_SECTOR_SIZE is defined, we support
partitioning/filesystems that use a larger "virtual" sector than the
logical sector. typically this matches the physical sector size of the
drive, which means that despite a small logical sector size, all I/O
is done in terms of the physical sector size.
Therefore, when MAX_VIRT_SECTOR_SIZE and MAX_PHYS_SECTOR_SIZE are
enabled (currently only ipod5g and ipod6g), prefer software-based
partial sector I/O.
Change-Id: I0815ad0a2f987b89bb2debfbf3d0ed64cdf85525
9bf033dd66