Set the clock during probe and keep its control during suspend / resume
operations.
This fixes an issue when CONFIG_PM is not set and where the clock is
never enabled.

Make use of devm_ functions to simplify the code.
Signed-off-by: Fabien Dessenne <fabien.dessenne@foss.st.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20211011135836.1045437-1-fabien.dessenne@foss.st.com