[POWERPC] iseries: remove some gcc 4.1 warnings

gcc 4.1 produces some warnings that say it is ignoring the packed
attribute on some structure elements, so, since all the elements of
these structs are packed, pack the structs instead.

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