pico-imx6ul: Add NFS boot support

Add script for retrieving the kernel via TFTP and mounting the
rootfs via NFS.

Signed-off-by: Diego Dorta <diego.dorta@nxp.com>
Acked-by: Fabio Estevam <fabio.estevam@nxp.com>

include/configs/pico-imx6ul.h

@@ -102,7 +102,31 @@
 			"bootz ${loadaddr} - ${fdt_addr}; " \
 		"else " \
 			"echo WARN: Cannot load the DT; " \
-		"fi;\0"
+		"fi;\0" \
+	"netargs=setenv bootargs console=${console},${baudrate} " \
+		"root=/dev/nfs " \
+	"ip=dhcp nfsroot=${serverip}:${nfsroot},v3,tcp\0" \
+		"netboot=echo Booting from net ...; " \
+		"run netargs; " \
+		"if test ${ip_dyn} = yes; then " \
+			"setenv get_cmd dhcp; " \
+		"else " \
+			"setenv get_cmd tftp; " \
+		"fi; " \
+		"${get_cmd} ${image}; " \
+		"if test ${boot_fdt} = yes || test ${boot_fdt} = try; then " \
+			"if ${get_cmd} ${fdt_addr} ${fdt_file}; then " \
+				"bootz ${loadaddr} - ${fdt_addr}; " \
+			"else " \
+				"if test ${boot_fdt} = try; then " \
+					"bootz; " \
+				"else " \
+					"echo WARN: Cannot load the DT; " \
+				"fi; " \
+			"fi; " \
+		"else " \
+			"bootz; " \
+		"fi;\0" \
 
 #define CONFIG_BOOTCOMMAND \
 	   "if mmc rescan; then " \