PCI: replace cfg space size (256/4096) by macros.

This is a cleanup that changes all PCI configuration space size
representations to the macros (PCI_CFG_SPACE_SIZE and
PCI_CFG_SPACE_EXP_SIZE). And the macros are also moved from
drivers/pci/probe.c to drivers/pci/pci.h.

Signed-off-by: Yu Zhao <yu.zhao@intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>