docs: update link to perf wiki

https://perf.wiki.kernel.org/ is now a permanent http redirect to
https://perfwiki.github.io/, which itself is an html redirect to
https://perfwiki.github.io/main/, but let's just link to the root and
let the second redirection be a detail on their side.

Since the second redirection is not an http redirection, it won't light
up the linkcheck, so we don't have to add an equivalent line to what was
previously there.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31824>

docs/drivers/llvmpipe.rst

@@ -237,7 +237,7 @@ Linux perf integration
 ~~~~~~~~~~~~~~~~~~~~~~
 
 On Linux, it is possible to have symbol resolution of JIT code with
-`Linux perf <https://perf.wiki.kernel.org/>`__:
+`Linux perf <https://perfwiki.github.io/main/>`__:
 
 ::