printk: remove deferred printing

Since printing occurs either atomically or from the printing
kthread, there is no need for any deferring or tracking possible
recursion paths. Remove all printk defer functions and context
tracking.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>