Several fixes for the AVR32 PATA driver

Several fixes for the AVR32 PATA driver:

* Updated to use new AVR32 SMC timing API. This removes the need for "magic"
constants in signal timing.

* Removed the ATA_FLAG_PIO_POLLING, the driver should use interrupts.

* Removed .port_disable and .irq_ack as these are no longer needed.

* Improved some comments.

Signed-off-by: Kristoffer Nyborg Gregertsen <kngregertsen@norway.atmel.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>