Add SPI NAND's bootloader and its booting parameters.

bsp/nuvoton/nk-980iot/uboot/env.txt

@@ -0,0 +1,7 @@
+baudrate=115200
+bootdelay=1
+stderr=serial
+stdin=serial
+stdout=serial
+loadrtt=nand read 0x80000000 0x200000 0x100000
+bootcmd=run loadrtt;go 0x0