ata: pata_parport-bpck6: move ppc6_wait_for_fifo to bpck6.c and rename

Move ppc6_wait_for_fifo to bpck6.c and rename it to bpck6_wait_for_fifo

Signed-off-by: Ondrej Zary <linux@zary.sk>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>