perf docs: Update link to AMD documentation

perf docs: Update link to AMD documentation

This updates the link to documentation on AMD processors.  The new link
points to a page where users can find the Processor Programming
Reference (PPR) documents for the family and model codes corresponding
to processors they are using.

Signed-off-by: Sandipan Das <sandipan.das@amd.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Ananth Narayan <ananth.narayan@amd.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Kim Phillips <kim.phillips@amd.com>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: Robert Richter <rrichter@amd.com>
Cc: Santosh Shukla <santosh.shukla@amd.com>
Link: https://lore.kernel.org/r/20211123084613.243792-2-sandipan.das@amd.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>