counter: intel-qep: Mark PM callbacks with __maybe_unused

Remove CONFIG_PM ifdef and mark PM callbacks with __maybe_unused.

Suggested-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Acked-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Link: https://lore.kernel.org/r/20210611115558.796338-1-jarkko.nikula@linux.intel.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>