sh: fix pci io access for r2d boards

Use generic_io_base to point out the pci io window, and make sure the
highest port address used is SH7751_PCI_IO_SIZE - 1.

This patch fixes pci io port access for the r2d boards - CONFIG_8139TOO_PIO
now works as expected. So does the alsa driver for CMI8738.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Acked-by: Katsuya MATSUBARA <matsu@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>