[POWERPC] iseries: Define insw et al. so libata/ide will compile

These are build fixes that enable (for example) libata and the ide
code to actually build on iSeries.  The associated hardware will never
be supported on legacy iSeries, so the code paths don't actually need
to work, but it is useful (especially for a combined kernel) if the
code can build.

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