ahci: Convert driver to use modern PM hooks

In order to add support for runtime PM to the ahci driver we first need to
convert the driver to use modern non-legacy system suspend hooks. There
should be no functional changes.

tj: Updated .driver.pm init for older compilers as suggested by Andy
    and Chrsitoph.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Tejun Heo <tj@kernel.org>