PCI: rcar: Convert to use generic config accessors

Convert the rcar-gen2 host PCI driver to use the generic config access
functions.

This changes the I/O accessors from io(read|write)X to readX/writeX
variants which are equivalent on ARM.

Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
CC: Simon Horman <horms@verge.net.au>
CC: linux-sh@vger.kernel.org