powerpc: Fix modular build of ide-pmac when mediabay is built in

Now that the powermac IDE host driver can be modular, we need to
export check_media_bay_by_base() and media_bay_set_ide_infos()
from drivers/macintosh/mediabay.c for it.

This fixes the following build error:

> CC [M]  drivers/ide/pmac.o
> drivers/ide/pmac.c: In function ‘pmac_ide_init_dev’:
> drivers/ide/pmac.c:955: error: implicit declaration of function
> ‘check_media_bay_by_base’
> drivers/ide/pmac.c: In function ‘pmac_ide_setup_device’:
> drivers/ide/pmac.c:1090: error: implicit declaration of function
> ‘media_bay_set_ide_infos’
> make[2]: *** [drivers/ide/pmac.o] Error 1
> make[1]: *** [drivers/ide] Error 2
> make: *** [drivers] Error 2

Reported-by: Subrata Modak <subrata@linux.vnet.ibm.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>