x86/crash: force unlock console before printing on kexec crash

x86/crash: force unlock console before printing on kexec crash

There is a small window where shootdown NMI might come to a CPU
(e.g. in serial interrupt handler) where console lock is taken. In order
not to leave following console prints waiting infinitely for shot down
CPUs to free the lock - force unlock the console.

The race has been frequently observed while crashing nested Xen in
an HVM domain.

Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: 7d5247cee21aa38a16c4b21bc9243eda70c8aebd
master date: 2019-10-02 11:25:05 +0100