spi: lpspi: Remove CONFIG_PM_SLEEP ifdefery

Use __maybe_unused for the suspend()/resume() hooks and get rid of
the CONFIG_PM_SLEEP ifdefery to improve the code.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Link: https://lore.kernel.org/r/20200817235812.19518-1-festevam@gmail.com


Signed-off-by: Mark Brown <broonie@kernel.org>