libata/pdc_adma: make SFF EH handle non-bmdma SFF drivers and standardize pdc_adma ops

libata/pdc_adma: make SFF EH handle non-bmdma SFF drivers and standardize pdc_adma ops

pdc_adma has interface similar to SFF but has its own DMA interface.
It currently implements noop bmdma ops to avoid crashing
ata_bmdma_error_handler() which BTW actually is EH for SFF drivers.

This patch makes ata_bmdma_error_handler() dereference bmdma ops iff
bmdma_addr is initialized as done in ata_bmdma_post_internal_cmd.
This change allows pdc_adma to standardize ops and use SFF
error_handler and post_internal_cmd.

Signed-off-by: Tejun Heo <[email protected]>
Cc: Mark Lord <[email protected]>
Signed-off-by: Jeff Garzik <[email protected]>