[POWERPC] Remove ppc_md.pci_map_irq & ppc_swizzle for ARCH=powerpc

These were inherited from ARCH=ppc, but are not needed since parsing of interrupts
should be done via the of_* functions (who can do swizzling). If we ever need to
do non-standard swizzling on bridges without a device-node, then we might add
back a slightly different version of ppc_md.pci_swizzle but for now, that is not
the case.

I removed the couple of calls for these in 83xx. If that breaks something, then
there is a problem with the device-tree on these.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>