sh: hook in struct pci_channel in sysdata

Store a struct pci_channel pointer in bus->sysdata. This makes whatever
struct pci_channel assigned to a bus available for sh4_pci_read() and
sh4_pci_write(). We also modify PCIBIOS_MIN_IO and PCIBIOS_MIN_MEM to
use bus->sysdata - this to gives us support for multiple pci channels.

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