AHCI/SILI - Send dummy SETXFER mode even though it is SATA

AHCI/SILI - Send dummy SETXFER mode even though it is SATA

* If the identify structure contains a non-zero/non-FFFF dmamode field
  we send a dummy SETXFER mode command to the device.

* Most SATA DISK devices set this field to 0 or FFFF and in this case no
  SETXFER mode command is sent.  SETXFER is non-applicable to SATA in
  general.

  Most ATAPI devices still initialize the dmamode field and some ATAPI
  devices still require SETXFER to be sent even though they are native SATA.

  SATA->PATA converters may require a SETXFER to be passed through before
  the PATA devices will operate properly.  In this case the dmamode field
  will likely be initialized.