platform/chrome: cros_ec_spi: Set PROBE_PREFER_ASYNCHRONOUS

This driver often takes on the order of 10ms to start, but in some cases
as much as 600ms [1]. It shouldn't have many cross-device dependencies
to race with, nor racy access to shared state with other drivers, so
this should be a relatively low risk change.

This driver was pinpointed as part of a survey of top slowest initcalls
(i.e., are built in, and probing synchronously) on a lab of ChromeOS
systems.

[1] 600ms was especially surprising to me, so I checked a little deeper.
This driver is used to interface with Embedded Controllers besides just
the traditional laptop power-state controller -- it also interfaces with
some fingerprint readers, which may start up in parallel with the
kernel, or which may not even be present on some SKUs, despite having a
node for it. Thus, our time is wasted just timing out talking to it. At
least we can do that without blocking everyone else.

Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
Link: https://lore.kernel.org/r/20221101152132.v2.5.Ia458a69e1d592bfa4f04cde7018bbc7486f91a23@changeid

drivers/platform/chrome/cros_ec_spi.c

@@ -834,6 +834,7 @@ static struct spi_driver cros_ec_driver_spi = {
 		.name	= "cros-ec-spi",
 		.of_match_table = cros_ec_spi_of_match,
 		.pm	= &cros_ec_spi_pm_ops,
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
 	},
 	.probe		= cros_ec_spi_probe,
 	.remove		= cros_ec_spi_remove,