dt-bindings:iio:gyro:invensense,mpu3050: txt to yaml format conversion.

Very similar to the mpu6050 binding.
Only unusual element is the i2c-gate section.
Example tweaked a little to include a real device behind the gate.

As Rob Herring suggested, dropped use of explicit i2c-gate yaml
binding in favour of just using the i2c-controller.yaml binding
directly.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201128173343.390165-4-jic23@kernel.org