Instead of always following up "power on" with a "reset", only

Instead of always following up "power on" with a "reset", only
send a single reset during attach.  We have discovered that some
devices such as the built-in keyboard on the Thinkpad T14s Gen 6
don't like getting more than one reset sent or they become
unresponsive.

This has been in snaps for a while and hasn't caused any major
regressions so we are confident the extra reset is not needed on
most hardware.

feedback from kettenis@
ok deraadt@ mlarkin@