ARM: atmel: sama5d3xek: convert to generic board

Enable CONFIG_SYS_GENERIC_BOARD, so that we get rid of the following
warning on boot:

"Warning: Your board does not use generic board. Please read
doc/README.generic-board and take action. Boards not
upgraded by the late 2014 may break or be removed."
Signed-off-by: NBo Shen <voice.shen@atmel.com>
Tested-by: NJosh Wu <josh.wu@atmel.com>
Signed-off-by: NAndreas Bießmann <andreas.devel@googlemail.com>

include/configs/sama5d3xek.h

@@ -34,6 +34,8 @@
 #define CONFIG_CMD_BOOTZ
 #define CONFIG_OF_LIBFDT		/* Device Tree support */
 
+#define CONFIG_SYS_GENERIC_BOARD
+
 /* general purpose I/O */
 #define CONFIG_AT91_GPIO