spi: spi-fsl-lpspi: Switch to SYSTEM_SLEEP_PM_OPS()

spi: spi-fsl-lpspi: Switch to SYSTEM_SLEEP_PM_OPS()

Replace SET_SYSTEM_SLEEP_PM_OPS with its modern SYSTEM_SLEEP_PM_OPS()
alternative.

The combined usage of pm_ptr() and SYSTEM_SLEEP_PM_OPS()
allows the compiler to evaluate if the runtime suspend/resume() functions
are used at build time or are simply dead code.

This allows removing the __maybe_unused notation from the runtime
suspend/resume() functions.

Signed-off-by: Fabio Estevam <festevam@denx.de>
Link: https://patch.msgid.link/20240625002023.228235-2-festevam@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>