dt-bindings: ata: ahci-platform: Detach common AHCI bindings

In order to create a more sophisticated AHCI controller DT bindings let's
divide the already available generic AHCI platform YAML schema into the
platform part and a set of the common AHCI properties. The former part
will be used to evaluate the AHCI DT nodes mainly compatible with the
generic AHCI controller while the later schema will be used for more
thorough AHCI DT nodes description. For instance such YAML schemas design
will be useful for our DW AHCI SATA controller derivative with four clock
sources, two reset lines, one system controller reference and specific
max Rx/Tx DMA xfers size constraints.

Note the phys and target-supply property requirement is preserved in the
generic AHCI platform bindings because some platforms can lack of the
explicitly specified PHYs or target device power regulators.

Also note the SATA/AHCI ports properties have been moved to the
$defs-paragraph of the schemas. It's done in order to create the
extendable properties hierarchy such that particular AHCI-controller
could add vendor-specific port properties.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>