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/lib/zstd/zstd_common.c b/lib/zstd/zstd_common.c
index 9a217e1..6b2c79e 100644
--- a/lib/zstd/zstd_common.c
+++ b/lib/zstd/zstd_common.c
@@ -9,6 +9,7 @@
 ***************************************/
 #include "error_private.h"
 #include "zstd_internal.h" /* declaration of ZSTD_isError, ZSTD_getErrorName, ZSTD_getErrorCode, ZSTD_getErrorString, ZSTD_versionNumber */
+#include <malloc.h>
 #include <linux/kernel.h>
 
 /*=**************************************************************