CONFIG_SCHED_DEBUG is the build-time Kconfig knob, the boot param
sched_debug and the /debug/sched/debug_enabled knobs control the
sched_debug_enabled variable, but what they really do is make
SCHED_DEBUG more verbose, so rename the lot.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>