Documentation: admin-guide: pm: Add documentation for agent_types

Add documentation to describe agent_types attribute.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20250508230250.1186619-3-srinivas.pandruvada@linux.intel.com
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

Author: spandruvada

Documentation/admin-guide/pm/intel_uncore_frequency_scaling.rst

@@ -97,6 +97,11 @@ Attributes in each directory:
 ``package_id``
 	This attribute is used to get the package id of this instance.
 
+``agent_types``
+	This attribute displays all the hardware agents present within the
+	domain. Each agent has the capability to control one or more hardware
+	subsystems, which include: core, cache, memory, and I/O.
+
 The other attributes are same as presented at package_*_die_* level.
 
 In most of current use cases, the "max_freq_khz" and "min_freq_khz"