sh: avoid using PCIBIOS_MIN_xxx

Replaces PCIBIOS_MIN_IO and PCIBIOS_MIN_MEM with direct struct
pci_channel access. This allows us to have more than one pci
channel.

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