ahci-platform: "Library-ise" suspend / resume functionality

Split suspend / resume code into host suspend / resume functionality and
resource enable / disabling phases, and export the new suspend_ / resume_host
functions.

tj: Minor comment formatting updates.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>