crypto: limit more FPU-enabled sections

Those crypto drivers use SSE/AVX/… for their crypto work and in order to
do so in kernel they need to enable the "FPU" in kernel mode which
disables preemption.
There are two problems with the way they are used:
- the while loop which processes X bytes may create latency spikes and
  should be avoided or limited.
- the cipher-walk-next part may allocate/free memory and may use
  kmap_atomic().

The whole kernel_fpu_begin()/end() processing isn't probably that cheap.
It most likely makes sense to process as much of those as possible in one
go. The new *_fpu_sched_rt() schedules only if a RT task is pending.

Probably we should measure the performance those ciphers in pure SW
mode and with this optimisations to see if it makes sense to keep them
for RT.

This kernel_fpu_resched() makes the code more preemptible which might hurt
performance.

Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>