rcu: Call touch_nmi_watchdog() while printing stall warnings

[ Upstream commit 3caa973b7a260e7a2a69edc94c300ab9c65148c3 ]

When RCU stall warning triggers, it can print out a lot of messages
while holding spinlocks.  If the console device is slow (e.g. an
actual or IPMI serial console), it may end up triggering NMI hard
lockup watchdog like the following.