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/nvme/nvme.c b/drivers/nvme/nvme.c
index 2593eb1..ef4382d 100644
--- a/drivers/nvme/nvme.c
+++ b/drivers/nvme/nvme.c
@@ -8,10 +8,12 @@
 #include <cpu_func.h>
 #include <dm.h>
 #include <errno.h>
+#include <malloc.h>
 #include <memalign.h>
 #include <pci.h>
 #include <time.h>
 #include <dm/device-internal.h>
+#include <linux/compat.h>
 #include "nvme.h"
 
 #define NVME_Q_DEPTH		2