piix/slc90e66: more tuneproc() fixing (take 2)

The tuneproc() method in both these drivers failed to set the drive's own speed.
Fix this by renaming the function and "wrapping around it" the new tuneproc()
method.  Switch back to calling tuneproc() in the PIO fallback code.
While at it, also convert the rest of the PIO timing code into proper C. :-)

Has been kind of tested on SLC90E66.  I'm too lazy to reboot my box and test
on ICH4... :-)

[ bart: I quickly tested it on ICH4. ]

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>