Add a new entry to the preemption menu which enables the real-time support
for the kernel. The choice is only enabled when an architecture supports
it.

It selects PREEMPT as the RT features depend on it. To achieve that the
existing PREEMPT choice is renamed to PREEMPT_LL which select PREEMPT as
well.

No functional change.
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Acked-by: NPaul E. McKenney <paulmck@linux.ibm.com>
Acked-by: NSteven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: NClark Williams <williams@redhat.com>
Acked-by: NDaniel Bristot de Oliveira <bristot@redhat.com>
Acked-by: NFrederic Weisbecker <frederic@kernel.org>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: NMarc Zyngier <marc.zyngier@arm.com>
Acked-by: NDaniel Wagner <wagi@monom.org>
Acked-by: NLuis Claudio R. Goncalves <lgoncalv@redhat.com>
Acked-by: NJulia Cartwright <julia@ni.com>
Acked-by: NTom Zanussi <tom.zanussi@linux.intel.com>
Acked-by: NGratian Crisan <gratian.crisan@ni.com>
Acked-by: NSebastian Siewior <bigeasy@linutronix.de>
Cc: Andrew Morton <akpm@linuxfoundation.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Tejun Heo <tj@kernel.org>
Link: http://lkml.kernel.org/r/alpine.DEB.2.21.1907172200190.1778@nanos.tec.linutronix.deSigned-off-by: NIngo Molnar <mingo@kernel.org>