Resurrect IT8172 IDE controller driver

Resurrect IT8172 IDE controller driver

Support for the IT8172 IDE controller was removed from the kernel
sometime after 2.6.18.  Support for the only boards that used the IT8172
was removed from the kernel after 2.6.18, as they had never compiled
since 2.6.0.  However, there are a couple of platforms that use this
chip: the PMC-Sierra Xiao Hu thin-client computer, which is no longer
in production, and the Linksys NSS4000 Network Attached Storage box,
which is based on the Xiao Hu board.  I am attempting to add support
for the Xiao Hu to the kernel, and this IT8172 IDE controller is the
first bit of code in this effort.

This patch resurrects the IT8172 IDE controller code.  I began with
the 2.6.18 version of the it8172.c file, and have moved it forward so
that it works with the latest version of the kernel.  I have run this
driver on a PMC-Sierra Xiao Hu board with the 2.6.28 kernel, and
I have had no problems with it in my configuration.  The attached patch
applies cleanly against 2.6.28.

Signed-off-by: Shane McDonald <mcdonald.shane@gmail.com>
Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Cc: alan@lxorguk.ukuu.org.uk
[bart: s/HWIF(drive)/drive->hwif/]
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>