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_mtk.c b/drivers/serial/serial_mtk.c
index 18530a4..e63f230 100644
--- a/drivers/serial/serial_mtk.c
+++ b/drivers/serial/serial_mtk.c
@@ -15,6 +15,7 @@
 #include <watchdog.h>
 #include <asm/io.h>
 #include <asm/types.h>
+#include <linux/err.h>
 
 struct mtk_serial_regs {
 	u32 rbr;
@@ -454,4 +455,4 @@
 
 DEBUG_UART_FUNCS
 
-#endif
\ No newline at end of file
+#endif