ata: ahci_brcmstb: add a quirk for MIPS-based platforms

Whereas ARM-based platforms have four phy interface registers and
information, the MIPS-based platforms have only three registers, and
there are no information and documentation. In the original BSP, It
using "strict-ahci" did not control these registers.

Signed-off-by: Jaedon Shin <jaedon.shin@gmail.com>
Tested-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Brian Norris <computersforpeace@gmail.com>