ata: ahci_brcm: Allow optional reset controller to be used

On BCM63138, we need to reset the AHCI core prior to start utilizing it,
grab the reset controller device cookie and do that.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>