ata: ahci_brcm: Fix AHCI resources management

The AHCI resources management within ahci_brcm.c is a little
convoluted, largely because it historically had a dedicated clock that
was managed within this file in the downstream tree. Once brough
upstream though, the clock was left to be managed by libahci_platform.c
which is entirely appropriate.

This patch series ensures that the AHCI resources are fetched and
enabled before any register access is done, thus avoiding bus errors on
platforms which clock gate the controller by default.

As a result we need to re-arrange the suspend() and resume() functions
in order to avoid accessing registers after the clocks have been turned
off respectively before the clocks have been turned on. Finally, we can
refactor brcm_ahci_get_portmask() in order to fetch the number of ports
from hpriv->mmio which is now accessible without jumping through hoops
like we used to do.

The commit pointed in the Fixes tag is both old and new enough not to
require major headaches for backporting of this patch.

Fixes: eba68f82

 ("ata: ahci_brcmstb: rename to support across Broadcom SoC's")
Cc: stable@vger.kernel.org
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>