dt-bindings: phy: Add UniPhier AHCI PHY description

Add DT bindings for PHY interface built into ahci controller implemented
in UniPhier SoCs.

Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1598352071-26675-2-git-send-email-hayashi.kunihiko@socionext.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>