sched/core: Use SCHED_RR in place of SCHED_FIFO for all users

Although SCHED_FIFO is a real-time scheduling policy, it can have bad
results on system latency, since each SCHED_FIFO task will run to
completion before yielding to another task. This can result in visible
micro-stalls when a SCHED_FIFO task hogs the CPU for too long. On a
system where latency is favored over throughput, using SCHED_RR is a
better choice than SCHED_FIFO.

Signed-off-by: Sultan Alsawaf <sultan@kerneltoast.com>
Signed-off-by: Oktapra Amtono <oktapra.amtono@gmail.com>
Signed-off-by: CloudedQuartz <ravenklawasd@gmail.com>