ata: pata_parport-bpck6: pass around struct pi_adapter *

Remove Interface typedef, pass around struct pi_adapter * down to all
functions instead. Remove PPCSTRUCT define.

Signed-off-by: Ondrej Zary <linux@zary.sk>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>