PCI: Move config space size macros to pci_regs.h

Move PCI configuration space size macros (PCI_CFG_SPACE_SIZE and
PCI_CFG_SPACE_EXP_SIZE) from drivers/pci/pci.h to
include/uapi/linux/pci_regs.h so they can be used by more drivers and
eliminate duplicate definitions.

[bhelgaas: Expand comment to include PCI-X details]
Signed-off-by: Wang Sheng-Hui <shhuiw@foxmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>