The base address of the PCI memory is 0x10000000 and the base address of the
PCI configuration space is 0x17000000 on the AR71xx SoCs.
The AR71XX_PCI_MEM_SIZE is defined as 0x08000000 which is wrong because that
overlaps with the configuration space. This patch fixes the value of the
AR71XX_PCI_MEM_SIZE constant, in order to avoid this resource conflicts.