debug: debug_stream: log per-core utilization from idle thread load

[kv2019i]

Keep the per-thread stack and cpu LOG_DBG print and add a separate LOG_INF that fires only for the Zephyr idle thread. The info-level print reports per-core CPU utilization calculated as the inverse of the idle thread load percentage.

[kv2019i]

This is very convenient debug tool especially when running with DP modules (the existing infra to track LL scheduler load don't provide the full picture anymore).

[150365.397958] <inf> copier: copier_comp_trigger: comp:0 0x6 No dai copier found, start/end offset is not calculated
[150365.397986] <wrn> host_comp: host_get_copy_bytes_normal: comp:0 0x6 no bytes to copy, available samples: 0, free_samples: 192
[150367.376058] <inf> thread_info: thread_info_cb: core 0 utilization 16%
[150369.377140] <inf> thread_info: thread_info_cb: core 0 utilization 15%
[150371.378221] <inf> thread_info: thread_info_cb: core 0 utilization 15%

Available when building SOF with "-o app/debug_stream_overlay.conf" and CONFIG_SOF_DEBUG_STREAM_THREAD_INFO=y

[Copilot]

Pull request overview

This PR enhances debug_stream thread reporting by adding a per-core CPU utilization info log derived from the Zephyr idle thread’s runtime stats, while keeping the existing per-thread debug log output.

Changes:

• Add <string.h> include (needed for string utilities used in the file).
• Emit a LOG_INF line for threads whose name starts with "idle", reporting utilization as 100% - idle_thread_cpu%.

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[Copilot]

The new utilization LOG_INF can print misleading 100% utilization when runtime stats are unavailable (e.g., CONFIG_THREAD_RUNTIME_STATS disabled, ud->stats_valid false, or k_thread_runtime_stats_get() fails and thread_info_cpu_utilization returns 0). Please guard this log on stats availability (and ideally on a distinct “cpu usage valid” result) so 0% idle isn’t conflated with “unknown” idle load.

Suggested change

	if (name && strncmp(name, "idle", 4) == 0)
	LOG_INF("core %u utilization %u%%", ud->core,
	100U - tinfo->cpu_usage * 100U / 255);
	#ifdef CONFIG_THREAD_RUNTIME_STATS
	if (ud->stats_valid && name && strncmp(name, "idle", 4) == 0) {
	LOG_INF("core %u utilization %u%%", ud->core,
	100U - tinfo->cpu_usage * 100U / 255);
	}
	#endif

[lgirdwood]

LGTM, can you respond to copilot. Thanks !