powerpc: move iSeries/iSeries_pci.h to platforms/iseries

The only real user of this file outside platforms/iseries was
drivers/net/iseries_veth.c but all it wanted was ISERIES_HV_ADDR()
so we move that to abs_addr.h (and lowercase it).

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