arm: a37xx: pci: Use standard register macros from pci.h

PCI config space of the aardvark PCIe Root Port is available only in
internal aardvark memory space starting at offset 0x0. PCI Express
registers (PCI_EXP_*) start at offset 0xc0. And Advanced Error Reporting
registers (PCI_ERR_*) start at offset 0x100.

Replace custom aardvark register macros by standard PCI macros from
include/pci.h file with fixed offset.

Some DEVCTL and AER macros are not defined in include/pci.h file, so define
them in the same way as in linux uapi header file pci_regs.h.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>