x86/traps: prevent interleaving of concurrent cpu state dumps

x86/traps: prevent interleaving of concurrent cpu state dumps

If two cpus enter show_execution_state() concurrently, the resulting console
output interleaved, and of no help debugging the situation further.

As calls to these locations are rare and usually important, it is acceptable
to serialise them.  These codepaths are also on the terminal error paths, so
the console lock must be the lock used for serialisation, to allow
console_force_unlock() to function properly.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>