spi: rockchip: enable autosuspend feature

If SPI is used for periodic polling any sensor, significant delays
sometimes appear. Switching on module clocks during resume lead to delays.
Enabling autosuspend mode causes the controller to not suspend between
SPI transfers and the delays disappear.
Signed-off-by: Alexander Kochetkov <al.kochet@gmail.com>
Link: https://lore.kernel.org/r/20201016085014.31667-1-al.kochet@gmail.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-rockchip.c

@@ -160,6 +160,8 @@
 #define ROCKCHIP_SPI_VER2_TYPE1			0x05EC0002
 #define ROCKCHIP_SPI_VER2_TYPE2			0x00110002
 
+#define ROCKCHIP_AUTOSUSPEND_TIMEOUT		2000
+
 struct rockchip_spi {
 	struct device *dev;
 
@@ -715,6 +717,8 @@ static int rockchip_spi_probe(struct platform_device *pdev)
 		goto err_disable_spiclk;
 	}
 
+	pm_runtime_set_autosuspend_delay(&pdev->dev, ROCKCHIP_AUTOSUSPEND_TIMEOUT);
+	pm_runtime_use_autosuspend(&pdev->dev);
 	pm_runtime_set_active(&pdev->dev);
 	pm_runtime_enable(&pdev->dev);