board/friendlyarm/nanopi-neo: refine genimage.cfg

This patch adds the offset argument for rootfs partiton so that it's
aligned to a 1MiB boundary, instead of using the size of the previous
u-boot partition to achieve this.

Genimage will make sure no partitions overlap. So we don't need a size
argument to limit the size of the u-boot image.

Signed-off-by: Dong Wang <wangdong115@foxmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

board/friendlyarm/nanopi-neo/genimage.cfg

@@ -7,11 +7,11 @@ image sdcard.img {
 		in-partition-table = false
 		image = "u-boot-sunxi-with-spl.bin"
 		offset = 8K
-		size = 1016K # 1MB - 8KB(offset)
 	}
 
 	partition rootfs {
 		partition-type = 0x83
 		image = "rootfs.ext4"
+		offset = 1M
 	}
 }