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/arch/x86/cpu/intel_common/itss.c b/arch/x86/cpu/intel_common/itss.c
index 9df51ad..fb30984 100644
--- a/arch/x86/cpu/intel_common/itss.c
+++ b/arch/x86/cpu/intel_common/itss.c
@@ -13,6 +13,7 @@
 #include <dm.h>
 #include <dt-structs.h>
 #include <irq.h>
+#include <malloc.h>
 #include <p2sb.h>
 #include <spl.h>
 #include <asm/itss.h>