ide: add IDE_HFLAG_CLEAR_SIMPLEX host flag

* Rename 'simplex_stat' variable to 'dma_stat' in ide_get_or_set_dma_base().

* Factor out code for forcing host out of "simplex" mode from
  ide_get_or_set_dma_base() to ide_pci_clear_simplex() helper.

* Add IDE_HFLAG_CLEAR_SIMPLEX host flag and set it in alim15x3 (for M5229),
  amd74xx (for AMD 7409), cmd64x (for CMD643), generic (for Netcell) and
  serverworks (for CSB5) host drivers.

* Make ide_get_or_set_dma_base() test for IDE_HFLAG_CLEAR_SIMPLEX host flag
  instead of checking dev->device (BTW the code was buggy because it didn't
  check for dev->vendor, luckily none of these PCI Device IDs was used by
  some other vendor for PCI IDE controller).

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
diff --git a/drivers/ide/pci/amd74xx.c b/drivers/ide/pci/amd74xx.c
index 13c9f67..2e8cbca 100644
--- a/drivers/ide/pci/amd74xx.c
+++ b/drivers/ide/pci/amd74xx.c
@@ -295,6 +295,7 @@
 	if (idx == 1) {
 		if (dev->revision <= 7)
 			d.swdma_mask = 0;
+		d.host_flags |= IDE_HFLAG_CLEAR_SIMPLEX;
 	} else if (idx == 4) {
 		if (dev->subsystem_vendor == PCI_VENDOR_ID_AMD &&
 		    dev->subsystem_device == PCI_DEVICE_ID_AMD_SERENADE)