MAINTAINERS: Expand and relocate PGO entry

MAINTAINERS: Expand and relocate PGO entry

This expands the "PGO" acronym and adds additional metadata to help have
patches get directed correctly.

Suggested-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/lkml/20210601190541.1446239-1-keescook@chromium.org
Acked-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Bill Wendling <wcw@google.com>
Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: clang-built-linux@googlegroups.com
Signed-off-by: Kees Cook <keescook@chromium.org>