sh: pci: Kill off platform-specific multi-window mappings.

Commit 68b42d1b ("sh: sh7785lcr: Map
whole PCI address space.") changed around the semantics of how various
chip-selects are made accessible to PCI. Now that there is a single
large mapping covering from CS0-CS6, there is no longer any need to
do multi-window mapping. Subsequently, all of the differing
implementations can be consolidated in to pci-sh7780.

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