sata_dwc_460ex: fix most of the sparse warnings

There are a lot sparse warnings. Most of them related to __iomem keyword which
sometimes absent when it's needed and vise versa.

The patch fixes most of the warnings.

While at it, remove the redundant sata_dwc_sht.can_queue
initialization to ATA_DEF_QUEUE.

tj: Added description about ATA_DEF_QUEUE init removal.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Tejun Heo <tj@kernel.org>