dt-bindings: regulator: mark regulator-suspend-microvolt as deprecated

dt-bindings: regulator: mark regulator-suspend-microvolt as deprecated

The Documentation/devicetree/bindings/regulator/regulator.yaml
already states in its description that regulator-suspend-microvolt
is deprecated, but the schema did not formally mark it as such.

Add the `deprecated: true` annotation to regulator-suspend-microvolt
so that this is enforced at the schema level.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Link: https://patch.msgid.link/20260119-regulator-binding-v1-1-e55d33b4c3e3@nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>