dp: switch the lock to use sys_sem

[lyakh]

sys_sem semaphores don't invoke a syscall in uncongested cases. Switch over to it to reduce syscall number.

[lgirdwood]

Nice cleanup, we probably want to use sys_sem in other places too and if so we could put the macros in a header for easier sharing.

[softwarecki]

The sys_sem object embeds a k_futex, so the syscall and k_object_find usage remain analogous to the previous implementation. There is an optimization because the syscall is invoked only when the calling thread must sleep while waiting for the semaphore to become available, which avoids syscall overhead in the uncontended fast path. Additionally, when userspace is disabled, the code falls back to using k_sem directly. The change therefore looks beneficial.