ata: ahci_brcmstb: enable support for ALPM

Enable support for ALPM in the host controller's capabilities
register. Also adjust the PLL  timeout to give it enough time
to lock when the port exits slumber mode.

tj: minor style updates

Signed-off-by: Danesh Petigara <dpetigara@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>