m68k: common PCI support definitions and code

Basic set of definitions and support code required to turn on CONFIG_PCI
for the m68k architecture. Nothing specific to any PCI implementation in
any m68k class CPU hardware yet.

Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>