tools/power turbostat: Document GNR UncMHz domain convention

Document that on Intel Granite Rapids Systems,
Uncore domains 0-2 are CPU domains, and
uncore domains 3-4 are IO domains.

Signed-off-by: Len Brown <[e-mail]>

tools/power/x86/turbostat/turbostat.8

···
 \fBUncMHz\fP per-package uncore MHz, instantaneous sample.
 .PP
 \fBUMHz1.0\fP per-package uncore MHz for domain=1 and fabric_cluster=0, instantaneous sample.  System summary is the average of all packages.
+Intel Granite Rapids systems use domains 0-2 for CPUs, and 3-4 for IO, with cluster always 0.
 For the "--show" and "--hide" options, use "UncMHz" to operate on all UMHz*.* as a group.
 .SH TOO MUCH INFORMATION EXAMPLE
 By default, turbostat dumps all possible information -- a system configuration header, followed by columns for all counters.