[POWERPC] iSeries: Eliminate "exceeds stub group size" warnings

Commit 3ccfc65c

 missed the same fixes for
legacy iSeries specific code, so make some more symbols no longer global.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>