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>
diff --git a/lib/Kconfig b/lib/Kconfig
index 32f3e5a..0058927 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -19,6 +19,9 @@
 config GENERIC_FIND_FIRST_BIT
 	bool
 
+config GENERIC_IOMAP
+	bool
+
 config CRC_CCITT
 	tristate "CRC-CCITT functions"
 	help