ata: libahci: Discard redundant force_port_map parameter

ata: libahci: Discard redundant force_port_map parameter

Currently there are four port-map-related fields declared in the
ahci_host_priv structure and used to setup the HBA ports mapping. First
the ports-mapping is read from the PI register and immediately stored in
the saved_port_map field. If forced_port_map is initialized with non-zero
value then its value will have greater priority over the value read from
PI, thus it will override the saved_port_map field. That value will be
then masked by a non-zero mask_port_map field and after some sanity checks
it will be stored in the ahci_host_priv.port_map field as a final port
mapping.

As you can see the logic is a bit too complicated for such a simple task.
We can freely get rid from at least one of the fields with no change to
the implemented semantic. The force_port_map field can be replaced with
taking non-zero saved_port_map value into account. So if saved_port_map is
pre-initialized by the low level drivers (platform drivers) then it will
have greater priority over the value read from PI register and will be
used as actual HBA ports mapping later on. Thus the ports map forcing task
will be just transferred from force_port_map to the saved_port_map field.

This modification will perfectly fit into the feature of having OF-based
initialization of the HW-init HBA CSR fields we are about to introduce in
the next commit.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>