mmc: pwrseq_simple: include deferred probe reasons

This adds a reason to /sys/kernel/debug/devices_deferred, which makes
it easier to debug deferred probes such as [0].

0. https://lore.kernel.org/all/20221228140708.26431-1-tom@tom-fitzhenry.me.uk/



Signed-off-by: Tom Fitzhenry <tom@tom-fitzhenry.me.uk>
Link: https://lore.kernel.org/r/20221228142354.28454-1-tom@tom-fitzhenry.me.uk


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