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/i2c/imx_lpi2c.c b/drivers/i2c/imx_lpi2c.c
index c9d3faa..62e6804 100644
--- a/drivers/i2c/imx_lpi2c.c
+++ b/drivers/i2c/imx_lpi2c.c
@@ -13,6 +13,7 @@
 #include <dm.h>
 #include <fdtdec.h>
 #include <i2c.h>
+#include <dm/device_compat.h>
 
 #define LPI2C_FIFO_SIZE 4
 #define LPI2C_NACK_TOUT_MS 1