regulator: Add labibb regulator binding

Adding the devicetree binding for labibb regulator.

 [sumits: cleanup as per review comments and update to yaml]

Signed-off-by: Nisha Kumari <nishakumari@codeaurora.org>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200622124110.20971-3-sumit.semwal@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>