[POWERPC] iseries: Make HvLpConfig_get(Primary)LpIndex functions

HvLpConfig_get(Primary)LpIndex are currently static inlines that return
fields from the itLpNaca, if we make them real functions we can make the
itLpNaca private to iSeries.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>