exec: don't include hw/boards for linux-user

As noted by Andreas, hw/boards.h shouldn't be used outside softmmu code.
Include it conditionally, and drop the (now unnecessary) ifdef guards in
hw/boards.h

Reported-by: Andreas Färber <afaerber@suse.de>
Cc: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Andreas Färber <afaerber@suse.de>

exec.c

@@ -26,7 +26,9 @@
 #include "cpu.h"
 #include "tcg.h"
 #include "hw/hw.h"
+#if !defined(CONFIG_USER_ONLY)
 #include "hw/boards.h"
+#endif
 #include "hw/qdev.h"
 #include "qemu/osdep.h"
 #include "sysemu/kvm.h"

include/hw/boards.h

@@ -3,8 +3,6 @@
 #ifndef HW_BOARDS_H
 #define HW_BOARDS_H
 
-#if !defined(CONFIG_USER_ONLY)
-
 #include "qemu/typedefs.h"
 #include "sysemu/blockdev.h"
 #include "sysemu/accel.h"
@@ -158,5 +156,3 @@ struct MachineState {
 };
 
 #endif
-
-#endif