powerpc: pci config cleanup

Choosing PCI or not at config time is allowed on some
platforms via an if expression in arch/powerpc/Kconfig.
To add a new platform with PCI support selectable at
config time, you must change the if expression.  This
patch makes this easier by changing:
    bool "PCI support" if <long expression>
to
    bool "PCI support" if PPC_PCI_CHOICE
and adding select PPC_PCI_CHOICE to all the config nodes that
were previously in the PCI if expression.

Platforms with unconditional PCI support continue to
just select PCI in their config nodes.

Signed-off-by: John Rigby <jrigby@freescale.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>