AHCI provides the register PORTS_IMPL to let the software know which port
is supported. The register must be initialized by the bootloader. However
in some cases u-boot doesn't properly initialize this value (if it is not
compiled with SATA support for example or if the SATA initialization fails).
The DTS entry "ports-implemented" can be used to override the value in
PORTS_IMPL.

Without this patch the SATA will not work in the following two cases:

* if there has been a failure to initialize SATA in u-boot.

* if ahci_platform module has been removed and re-inserted. The reason is
  that the content of PORTS_IMPL is lost after the module is removed.
  I suspect that it's because the controller is reset by the hwmod.

Cc: <stable@vger.kernel.org> # v4.6+
Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
Acked-by: Roger Quadros <rogerq@ti.com>
[tony@atomide.com: updated comments with what goes wrong]
Signed-off-by: Tony Lindgren <tony@atomide.com>