dt-bindings: ata: ahci-platform: Clarify common AHCI props constraints

Indeed in accordance with what is implemented in the AHCI platform driver
and the way the AHCI DT nodes are defined in the DT files we can add the
next AHCI DT properties constraints: AHCI CSR ID is fixed to 'ahci', PHY
name is fixed to 'sata-phy', AHCI controller can't have more than 32 ports
by design, AHCI controller can have up to 32 IRQ lines.

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