Shuttle KD20 has NAND flash with 0x20000 (128KiB) erase blocks.
Correctly set that in uboot-envtools as well to allow writing to the
bootloader environment using fw_setenv.
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
(cherry picked from commit fa676395136b17d753fd90137e58f02a4fcdb09e)