mmc: Drain the intrhook in mmc_detach()

Buggy SD card drivers may attach and detach a mmc(4) driver instance in
quick succession. In this case mmc(4) must disestablish its intrhook
callback during detach. Thus, this change adds a call to
config_intrhook_drain(), which blocks or does nothing if the intrhook is
running or has already ran (the SD card was plugged in), and
disestablishes the hook if it hasn't ran yet (the SD card was not
plugged in).

PR: 254373
Reviewed by: imp, manu, markj
MFC after: 1 week
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D31262