MLK-13311 configs: mx6sll_lpddr3_arm2: Enable network function

Since mx6sll has no ethernet controller, we take USB ethernet device as
network device by default.

Signed-off-by: Peter Chen <peter.chen@nxp.com>
(cherry picked from commit f6c75d01)

include/configs/mx6sll_arm2.h

@@ -109,6 +109,7 @@
 		"root=/dev/nfs " \
 	"ip=dhcp nfsroot=${serverip}:${nfsroot},v3,tcp\0" \
 		"netboot=echo Booting from net ...; " \
+		"usb start; " \
 		"run netargs; " \
 		"if test ${ip_dyn} = yes; then " \
 			"setenv get_cmd dhcp; " \
@@ -192,6 +193,10 @@
 #define CONFIG_ENV_SPI_MAX_HZ		CONFIG_SF_DEFAULT_SPEED
 #endif
 
+/* Network */
+#define CONFIG_CMD_PING
+#define CONFIG_CMD_DHCP
+
 /* USB Configs */
 #define CONFIG_CMD_USB
 #ifdef CONFIG_CMD_USB