ppc: fix #ifdef-s in mediabay driver (take 2)

* Replace incorrect CONFIG_BLK_DEV_IDE #ifdef in
  check_media_bay() by CONFIG_MAC_FLOPPY one.

* Replace incorrect CONFIG_BLK_DEV_IDE #ifdef-s by
  CONFIG_BLK_DEV_IDE_PMAC ones.

* check_media_bay() is used only by drivers/block/swim3.c
  so make this function available only if CONFIG_MAC_FLOPPY
  is defined.

* check_media_bay_by_base() and media_bay_set_ide_infos()
  are used only by drivers/ide/ppc/pmac.c so so make these
  functions available only if CONFIG_MAC_FLOPPY is defined.

v2:
* Remove ifdefs from function prototypes. (Andrew Morton)

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>