smp: change printks that occur every hotplug to pr_debugs

Hotplug occurs frequently enough on our targets that its messages are
clogging up the logs. There is no need for any messages to be printed
when hotplug is successful.

Change-Id: Icf213ab409ba428f39439f886cdf4c070a48bfbf
Signed-off-by: Jeff Ohlstein <johlstei@codeaurora.org>