dt-bindings: soc: samsung: exynos-pmu: add Exynos4212 compatible

dt-bindings: soc: samsung: exynos-pmu: add Exynos4212 compatible

Support for the Exynos4212 SoC was originally dropped as there were
no boards using it. We will be adding a device that uses it, so add
back the relevant compatible.

This reverts part of commit c40610198f35 ("soc: samsung: Remove
Exynos4212 related dead code").

Signed-off-by: Artur Weber <aweber.kernel@gmail.com>
Link: https://lore.kernel.org/r/20230501195525.6268-2-aweber.kernel@gmail.com
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>