mmc: sdhci-pci: Set PROBE_PREFER_ASYNCHRONOUS

This driver often takes on the order of 10ms to start, but in some cases
as much as 190ms. 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. We've done similarly with a
variety of other MMC host drivers already.

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.

Signed-off-by: Brian Norris <briannorris@chromium.org>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20221028155633.1.I6c4bfb31e88fad934e7360242cb662e01612c1bb@changeid


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>