[POWERPC] Make non-PCI build work again

Maple and pasemi both require PCI as does CONFIG_OF_PLATFORM_PCI.
The default setting of CONFIG_ISA_DMA_API is set to match the protection
around the relevant routines in asm/dma.h.

I also had to remove the PMAC platform from the combined build.  The
precis is that to build a 64 bit kernel with no PCI, you can only include
pSeries and iSeries.

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