ide: move ide_config_drive_speed() calls to upper layers (take 2)

* Convert {ide_hwif_t,ide_pci_device_t}->host_flag to be u16.

* Add IDE_HFLAG_POST_SET_MODE host flag to indicate the need to program 
  the host for the transfer mode after programming the device.  Set it
  in au1xxx-ide, amd74xx, cs5530, cs5535, pdc202xx_new, sc1200, pmac
  and via82cxxx host drivers.

* Add IDE_HFLAG_NO_SET_MODE host flag to indicate the need to completely
  skip programming of host/device for the transfer mode ("smart" hosts).
  Set it in it821x host driver and check it in ide_tune_dma().

* Add ide_set_pio_mode()/ide_set_dma_mode() helpers and convert all
  direct ->set_pio_mode/->speedproc users to use these helpers.

* Move ide_config_drive_speed() calls from ->set_pio_mode/->speedproc
  methods to callers.

* Rename ->speedproc method to ->set_dma_mode, make it void and update
  all implementations accordingly.

* Update ide_set_xfer_rate() comments.

* Unexport ide_config_drive_speed().

v2:
* Fix issues noticed by Sergei:
  - export ide_set_dma_mode() instead of moving ->set_pio_mode abuse wrt
    to setting DMA modes from sc1200_set_pio_mode() to do_special()
  - check IDE_HFLAG_NO_SET_MODE in ide_tune_dma()
  - check for (hwif->set_pio_mode) == NULL in ide_set_pio_mode()
  - check for (hwif->set_dma_mode) == NULL in ide_set_dma_mode()
  - return -1 from ide_set_{pio,dma}_mode() if ->set_{pio,dma}_mode == NULL
  - don't set ->set_{pio,dma}_mode on it821x in "smart" mode
  - fix build problem in pmac.c
  - minor fixes in au1xxx-ide.c/cs5530.c/siimage.c
  - improve patch description

Changes in behavior caused by this patch:
- HDIO_SET_PIO_MODE ioctl would now return -ENOSYS for attempts to change
  PIO mode if it821x controller is in "smart" mode
- removal of two debugging printk-s (from cs5530.c and sc1200.c)
- transfer modes 0x00-0x07 passed from user space may be programmed twice on
  the device (not really an issue since 0x00 is not supported correctly by
  any host driver ATM, 0x01 is not supported at all and 0x02-0x07 are invalid)

Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>