Simplify pci-ixp4xx.c driver code and use new PCI_CONF1_ADDRESS() macro for
accessing PCI config space.

Link: https://lore.kernel.org/r/20220928122539.15116-1-pali@kernel.orgTested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>