mips: switch to GENERIC_PCI_IOMAP

mips copied pci_iomap from generic code, probably to avoid
pulling the rest of iomap.c in.  Since that's in
a separate file now, we can reuse the common implementation.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index d46f1da..b70c96f 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -2317,6 +2317,7 @@
 	bool "Support for PCI controller"
 	depends on HW_HAS_PCI
 	select PCI_DOMAINS
+	select GENERIC_PCI_IOMAP
 	help
 	  Find out whether you have a PCI motherboard. PCI is the name of a
 	  bus system, i.e. the way the CPU talks to the other stuff inside