dp: Update file naming to better reflect implementation

Update the DP scheduler file name by replacing the proxy postfix to reflect
actual content and avoid misleading semantics. The file does not implement
any proxy layer, and it is also used when userspace is not active.
It contains only the native DP thread.

Signed-off-by: Adrian Warecki <adrian.warecki@intel.com>

Author: softwarecki

src/schedule/CMakeLists.txt

@@ -41,7 +41,7 @@ endif()
 if (CONFIG_SOF_USERSPACE_PROXY OR NOT CONFIG_USERSPACE)
 	zephyr_library_sources_ifdef(CONFIG_ZEPHYR_DP_SCHEDULER
 		zephyr_dp_schedule.c
-		zephyr_dp_schedule_proxy.c
+		zephyr_dp_schedule_thread.c
 	)
 else()
 	zephyr_library_sources_ifdef(CONFIG_ZEPHYR_DP_SCHEDULER