printk: allow disabling printk per-console device kthreads at boot
JIRA: https://issues.redhat.com/browse/RHEL-17709
Upstream Status: RHEL only
Create the 'printk_no_perconsole_kthreads' boot parameter, allowing one to disable the
per-console device printk kthreads, which are enabled by default.
Signed-off-by: Luis Claudio R. Goncalves lgoncalv@redhat.com