Add new config-devices.mak for each target

We generate config-devices.h from there automatically.
We need to do it in main Makefile, because we are going to need a main
Makefile for them.

Patchworks-ID: 35196
Signed-off-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/.gitignore b/.gitignore
index 7e6d844..cdd6aad 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,5 @@
+config-devices.*
+config-all-devices.*
 config-host.*
 config-target.*
 i386