Convert i2c-omap.txt to YAML schema for better checks and documentation.

Following properties were used in DT but were not documented in txt
bindings and has been included in YAML schema:
1. Include ti,am4372-i2c compatible
2. Document clocks property
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>