ide: convert ide-timing.h to ide-timings.c library (take 2)

ide: convert ide-timing.h to ide-timings.c library (take 2)

* Don't include ide-timing.h in cs5535 and sis5513 host drivers
  (they don't need it currently).

* Convert ide-timing.h to ide-timings.c library and add CONFIG_IDE_TIMINGS
  config option to be selected by host drivers using the library.

While at it:

- fix ide_timing_find_mode() placement

v2:
* Add missing EXPORT_SYMBOLs. (Stephen Rothwell <sfr@canb.auug.org.au>)

There should be no functional changes caused by this patch.

Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>