lib: move GENERIC_IOMAP to lib/Kconfig

define GENERIC_IOMAP in a central location
instead of all architectures. This will be helpful
for the follow-up patch which makes it select
other configs. Code is also a bit shorter this way.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

arch/m68k/Kconfig

@@ -38,9 +38,6 @@ config GENERIC_CALIBRATE_DELAY
 	bool
 	default y
 
-config GENERIC_IOMAP
-	def_bool MMU
-
 config TIME_LOW_RES
 	bool
 	default y
@@ -73,6 +70,7 @@ source "kernel/Kconfig.freezer"
 config MMU
 	bool "MMU-based Paged Memory Management Support"
 	default y
+	select GENERIC_IOMAP
 	help
 	  Select if you want MMU-based virtualised addressing space
 	  support by paged memory management. If unsure, say 'Y'.