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/Makefile.hw b/Makefile.hw
index 830902b..2b4ef03 100644
--- a/Makefile.hw
+++ b/Makefile.hw
@@ -1,6 +1,7 @@
 # Makefile for qemu target independent devices.
 
 include ../config-host.mak
+include ../config-all-devices.mak
 include config.mak
 include $(SRC_PATH)/rules.mak