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/mips/mach-pic32/cpu.c b/arch/mips/mach-pic32/cpu.c
index 8bb12a5..8075d93 100644
--- a/arch/mips/mach-pic32/cpu.c
+++ b/arch/mips/mach-pic32/cpu.c
@@ -7,6 +7,7 @@
 #include <common.h>
 #include <clk.h>
 #include <dm.h>
+#include <malloc.h>
 #include <mach/pic32.h>
 #include <mach/ddr.h>
 #include <dt-bindings/clock/microchip,clock.h>