docs/xentop: Add documentation for physical CPU monitoring feature

Add man page documentation for the new '-p/--pcpus' flag that displays
physical CPU utilization metrics. This provides hypervisor-level CPU
usage insights alongside existing domain statistics.

Changes include:
- Add '-p' flag to SYNOPSIS section
- Document '--pcpus' option with description
- Maintain consistency with existing documentation style

Signed-off-by: Jahan Murudi <jahan.murudi.zg@renesas.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Anthony PERARD <anthony.perard@vates.tech>
Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>

docs/man/xentop.1.pod

@@ -5,7 +5,7 @@ xentop - displays real-time information about a Xen system and domains
 =head1 SYNOPSIS
 
 B<xentop> [B<-h>] [B<-V>] [B<-d>SECONDS] [B<-n>] [B<-r>] [B<-v>] [B<-f>]
-[B<-b>] [B<-i>ITERATIONS] [B<-z>]
+[B<-b>] [B<-i>ITERATIONS] [B<-z>] [B<-p>]
 
 =head1 DESCRIPTION
 
@@ -61,6 +61,10 @@ maximum number of iterations xentop should produce before ending
 
 display dom0 first, ignoring interactive sorting
 
+=item B<-p>, B<--pcpus>
+
+display physical CPU utilization metrics
+
 =back
 
 =head1 INTERACTIVE COMMANDS