spi: atmel: remove #ifdef CONFIG_{PM, SLEEP}

Remove #ifdef CONFIG_PM, #ifdef CONFIG_PM_SLEEP and use
SYSTEM_SLEEP_PM_OPS() and RUNTIME_PM_OPS() macros instead which allows
getting also rid of __maybe_unused in the code.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20220718071052.1707858-1-claudiu.beznea@microchip.com
Signed-off-by: Mark Brown <broonie@kernel.org>