ide-pmac: remove dead code

Remove unused pmac_ide_{check_base,get_irq}() and pmac_find_ide_boot(),
then remove no longer needed ide_majors[] and pmac_ide_count.

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