ide: factor out simplex handling from ide_pci_dma_base()

* Factor out simplex handling from ide_pci_dma_base() to
  ide_pci_check_simplex().

* Set hwif->dma_base early in ->init_dma method / ide_hwif_setup_dma()
  and reset it in ide_init_port() if DMA initialization fails.

* Use ->read_sff_dma_status instead of ->INB in ide_pci_dma_base().

There should be no functional changes caused by this patch.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
diff --git a/include/linux/ide.h b/include/linux/ide.h
index 6d77460..a179a7f 100644
--- a/include/linux/ide.h
+++ b/include/linux/ide.h
@@ -1008,6 +1008,7 @@
 int ide_pci_set_master(struct pci_dev *, const char *);
 unsigned long ide_pci_dma_base(ide_hwif_t *, const struct ide_port_info *);
 extern const struct ide_dma_ops sff_dma_ops;
+int ide_pci_check_simplex(ide_hwif_t *, const struct ide_port_info *);
 int ide_hwif_setup_dma(ide_hwif_t *, const struct ide_port_info *);
 #else
 static inline int ide_hwif_setup_dma(ide_hwif_t *hwif,