pci: mpc85xx: Allow 8/16-bit access to PCI config space

This Freescale mpc85xx PCI controller should support 8-bit and 16-bit read
and write access to PCI config space as described in more Freescale
reference manuals.

This change fixes issue that 8-bit and 16-bit write to PCI config space
caused to clear adjacent bits of 32-bit PCI register.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Heiko Schocher <hs@denx.de>
Tested-by: Heiko Schocher <hs@denx.de>