MIPS: Expose missing pci_io{map,unmap} declarations

MIPS: Expose missing pci_io{map,unmap} declarations

The GENERIC_PCI_IOMAP does not depend on CONFIG_PCI so move
it to the CONFIG_MIPS symbol so it's always selected for MIPS.
This fixes the missing pci_iomap declaration for MIPS.
Moreover, the pci_iounmap function was not defined in the
io.h header file if the CONFIG_PCI symbol is not set,
but it should since MIPS is not using CONFIG_GENERIC_IOMAP.

This fixes the following problem on a allyesconfig:

drivers/net/ethernet/3com/3c59x.c:1031:2: error: implicit declaration of
function 'pci_iomap' [-Werror=implicit-function-declaration]
drivers/net/ethernet/3com/3c59x.c:1044:3: error: implicit declaration of
function 'pci_iounmap' [-Werror=implicit-function-declaration]

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Acked-by: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5478/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>