PM: wakeup: Add missing wakeup source attribute relax_count

There is wakeup source attribute 'active_count', but its counterpart
attribute 'relax_count' is missing.

Add 'relax_count' for consistency.

Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com>
Link: https://patch.msgid.link/20250505-add_power_attrs-v1-1-10bc3c73c320@quicinc.com


[ rjw: Changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>