dt-bindings: ata: Convert ti,dm816-ahci to DT schema

Convert the TI DM816 AHCI SATA Controller to DT schema format. It's a
straight-forward conversion.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>