spi: rpc-if: Drop deprecated SIMPLE_DEV_PM_OPS

spi: rpc-if: Drop deprecated SIMPLE_DEV_PM_OPS

Replace SIMPLE_DEV_PM_OPS->DEFINE_SIMPLE_DEV_PM_OPS macro and use
pm_sleep_ptr(). This lets us drop the check for CONFIG_PM_SLEEP, and
reduces kernel size in case CONFIG_PM or CONFIG_PM_SLEEP is disabled,
while increasing build coverage.

Also drop the __maybe_unused attribute from PM functions.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Link: https://patch.msgid.link/20250921112649.104516-2-biju.das.jz@bp.renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>