spi: atmel-quadspi: add runtime pm support

Add runtime PM support for atmel-quadspi which will disable/enable
QSPI clocks on proper runtime_suspend/runtime_resume ops.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20220609084246.1795419-2-claudiu.beznea@microchip.com
Signed-off-by: Mark Brown <broonie@kernel.org>