ahci_xgene: Fix the DMA state machine lockup for the ATA_CMD_PACKET PIO mode command.

This patch addresses the issue with ATA_CMD_PACKET pio mode
command for enumeration and device detection with ATAPI devices.
The X-Gene AHCI controller has an errata in which it cannot clear
the BSY bit after the PIO setup FIS. The dma state machine enters
CMFatalErrorUpdate state and locks up.

Signed-off-by: Suman Tripathi <stripathi@apm.com>
Signed-off-by: Tejun Heo <tj@kernel.org>