sh: Ignore 32-bit windows in 29-bit mode for SH7786 PCIe.

Certain memory windows are only available for 32-bit space, so skip over
these in 29-bit mode. This will severely restrict the amount of memory
that can be mapped, but since a boot loader bug makes booting in 29-bit
mode close to impossible anyways, everything is ok.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>