dt-bindings: reset: imx-src: Simplify compatible schema and drop unneeded quotes

dt-bindings: reset: imx-src: Simplify compatible schema and drop unneeded quotes

The compatible schema can be simplified to a single enum for all the cases
with "fsl,imx51-src" fallback compatible.

In addition, the compatible strings are redundantly quoted. Drop unneeded
quotes over simple string values to fix a soon to be enabled yamllint
warning:

  [error] string value is redundantly quoted with any quotes (quoted-strings)

Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20231122224404.2808838-1-robh@kernel.org
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>