spi: omap-spi: Convert to json-schema

Convert omap-spi dt-binding documentation from txt to yaml format.

Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210621092900.951-1-a-govindraju@ti.com


Signed-off-by: Mark Brown <broonie@kernel.org>