Simplify pcie-mt7621.c driver code and use new PCI_CONF1_EXT_ADDRESS()
macro for accessing PCIe config space.

Link: https://lore.kernel.org/r/20220924092404.31776-4-pali@kernel.orgSigned-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Acked-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>