dm: core: Require users of devres to include the header

At present devres.h is included in all files that include dm.h but few
make use of it. Also this pulls in linux/compat which adds several more
headers. Drop the automatic inclusion and require files to include devres
themselves. This provides a good indication of which files use devres.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Anatolij Gustschin <agust@denx.de>
diff --git a/drivers/serial/serial_zynq.c b/drivers/serial/serial_zynq.c
index 7e486a6..c073759 100644
--- a/drivers/serial/serial_zynq.c
+++ b/drivers/serial/serial_zynq.c
@@ -14,6 +14,7 @@
 #include <asm/io.h>
 #include <linux/compiler.h>
 #include <serial.h>
+#include <linux/err.h>
 
 DECLARE_GLOBAL_DATA_PTR;