dt-bindings: i2c: exynos5: Convert to dtschema

dt-bindings: i2c: exynos5: Convert to dtschema

Convert Samsung Exynos High Speed I2C bindings doc to DT schema format.

Changes during bindings conversion:
1. Added missing required clock properties (driver fails when it's
   unable to get the clock)
2. Removed properties and descriptions that can be found in
   schemas/i2c/i2c-controller.yaml [1]
3. Fixed the example so it can be validated by dtschema

[1] https://github.com/robherring/dt-schema/blob/master/schemas/i2c/i2c-controller.yaml

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>