ide: switch to DMA-mapping API part #2

Follow-up to commit 5c05ff68b9a9b40a9be949497e0aa980185565cf
("ide: switch to DMA-mapping API"):

* pci_{alloc,free}_consistent() -> dma_{alloc,free}_coherent()
  in ide_{allocate,release}_dma_engine().

* Add ->prd_max_nents and ->prd_ent_size fields to ide_hwif_t
  (+ set default values in ide_allocate_dma_engine()).

* Make ide_{allocate,release}_dma_engine() available also
  for CONFIG_BLK_DEV_IDEDMA_SFF=n.  Then convert au1xxx-ide.c,
  scc_pata.c and sgiioc4.c to use them.

* Add missing ->init_dma method to scc_pata.

This patch also fixes:
- ->dmatable_cpu leak for au1xxx-ide
- too early realease of ->dmatable_cpu for scc_pata
- wrong amount of ->dmatable_cpu memory being freed for sgiioc4

While at it:
- remove superfluous ->dma_base check from ide_unregister()
- return -ENOMEM on error in ide_release_dma_engine()
- beautify error message in ide_release_dma_engine()

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
diff --git a/drivers/ide/mips/au1xxx-ide.c b/drivers/ide/mips/au1xxx-ide.c
index f9e88cf..0ec8fd1 100644
--- a/drivers/ide/mips/au1xxx-ide.c
+++ b/drivers/ide/mips/au1xxx-ide.c
@@ -427,10 +427,9 @@
 							     NUM_DESCRIPTORS);
 	auide->rx_desc_head = (void*)au1xxx_dbdma_ring_alloc(auide->rx_chan,
 							     NUM_DESCRIPTORS);
- 
-	hwif->dmatable_cpu = dma_alloc_coherent(hwif->dev,
-						PRD_ENTRIES * PRD_BYTES,        /* 1 Page */
-						&hwif->dmatable_dma, GFP_KERNEL);
+
+	/* FIXME: check return value */
+	(void)ide_allocate_dma_engine(hwif);
 	
 	au1xxx_dbdma_start( auide->tx_chan );
 	au1xxx_dbdma_start( auide->rx_chan );