New variants of devm_clk_get() for prepared and enabled clocks

These two patches create a set of new devm helpers that return clocks
already prepared or prepared-and-enabled. The automatic cleanup cares
for unpreparing and disabling+unpreparing respectively.

This allows to simplify various drivers as was demonstrated with
additional patches sent with the various revisions of this patch set.
See
https://lore.kernel.org/r/20210510174142.986250-1-u.kleine-koenig@pengutronix.de
for the last submission round. This pull request doesn't contain these
patches though.
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