dm: core: Create a new header file for 'compat' features

At present dm/device.h includes the linux-compatible features. This
requires including linux/compat.h which in turn includes a lot of headers.
One of these is malloc.h which we thus end up including in every file in
U-Boot. Apart from the inefficiency of this, it is problematic for sandbox
which needs to use the system malloc() in some files.

Move the compatibility features into a separate header file.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/mtd/ubi/misc.c b/drivers/mtd/ubi/misc.c
index 685324d..3f7ee59 100644
--- a/drivers/mtd/ubi/misc.c
+++ b/drivers/mtd/ubi/misc.c
@@ -7,6 +7,7 @@
 
 /* Here we keep miscellaneous functions which are used all over the UBI code */
 
+#include <malloc.h>
 #include <ubi_uboot.h>
 #include "ubi.h"