ata: ahci_brcmstb: rename to support across Broadcom SoC's

Rename the existing Broadcom STB ahci driver to common
Broadcom SATA3 driver to share this across Broadcom SoCs.

Signed-off-by: Yendapally Reddy Dhananjaya Reddy <yendapally.reddy@broadcom.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>