chrt: Add support for SCHED_FLAG_DL_OVERRUN

chrt: Add support for SCHED_FLAG_DL_OVERRUN

When set on a SCHED_DEADLINE task, the kernel sends SIGXCPU to the
task if it exceeds its runtime budget within a period. Without this
flag the task is silently throttled until the next period. Useful
for real-time applications that need to detect when they are not
meeting their timing requirements.

Add -O/--deadline-overrun option to allow users to toggle this
feature using the deadline scheduling class.

Signed-off-by: Furkan Caliskan <frn1furkan10@gmail.com>