sched_ext: Convert scx_dump_state() spinlock to raw spinlock

sched_ext: Convert scx_dump_state() spinlock to raw spinlock

The scx_dump_state() function uses a regular spinlock to serialize
access. In a subsequent patch, this function will be called while
holding scx_sched_lock, which is a raw spinlock, creating a lock
nesting violation.

Convert the dump_lock to a raw spinlock and use the guard macro for
cleaner lock management.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>