docs: ABI: sysfs-bus-event_source-devices-vpa-dtl: Document sysfs event format entries for vpa_dtl pmu

Details are added for the vpa_dtl pmu event and format
attributes in the ABI documentation.

Signed-off-by: Kajol Jain <kjain@linux.ibm.com>
Tested-by: Tejas Manhas <tejas05@linux.ibm.com>
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250915102947.26681-4-atrajeev@linux.ibm.com

Author: kjain101

Documentation/ABI/testing/sysfs-bus-event_source-devices-vpa-dtl

@@ -0,0 +1,25 @@
+What:           /sys/bus/event_source/devices/vpa_dtl/format
+Date:           February 2025
+Contact:        Linux on PowerPC Developer List <linuxppc-dev at lists.ozlabs.org>
+Description:    Read-only. Attribute group to describe the magic bits
+                that go into perf_event_attr.config for a particular pmu.
+                (See ABI/testing/sysfs-bus-event_source-devices-format).
+
+                Each attribute under this group defines a bit range of the
+                perf_event_attr.config. Supported attribute are listed
+                below::
+
+				event  = "config:0-7"  - event ID
+
+		For example::
+
+		  dtl_cede = "event=0x1"
+
+What:           /sys/bus/event_source/devices/vpa_dtl/events
+Date:           February 2025
+Contact:        Linux on PowerPC Developer List <linuxppc-dev at lists.ozlabs.org>
+Description:	(RO) Attribute group to describe performance monitoring events
+                for the Virtual Processor Dispatch Trace Log. Each attribute in
+		this group describes a single performance monitoring event
+		supported by vpa_dtl pmu.  The name of the file is the name of
+		the event (See ABI/testing/sysfs-bus-event_source-devices-events).