um: Use generic idle loop

Signed-off-by: Richard Weinberger <richard@nod.at>
Cc: user-mode-linux-devel@lists.sourceforge.net
Link: http://lkml.kernel.org/r/1366149209-24787-1-git-send-email-richard@nod.at


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>