use mke2fs instead of genext2fs for genimage

When genimage makes an SD card image, it uses genext2fs
by default to create the rootfs partition.
However, starting from commit 4618c08e2, the creation fails.
Use mke2fs instead.

Signed-off-by: carbon <carbon@milkv.io>

device/milkv-duo256m-glibc-arm64-sd/genimage.cfg

@@ -12,6 +12,7 @@ image boot.vfat {
 image rootfs.ext4 {
 	ext4 {
 		label = "rootfs"
+		use-mke2fs = true
 	}
 	size = 768M
 }

device/milkv-duo256m-musl-riscv64-sd/genimage.cfg

@@ -12,6 +12,7 @@ image boot.vfat {
 image rootfs.ext4 {
 	ext4 {
 		label = "rootfs"
+		use-mke2fs = true
 	}
 	size = 768M
 }

device/milkv-duos-glibc-arm64-sd/genimage.cfg

@@ -12,6 +12,7 @@ image boot.vfat {
 image rootfs.ext4 {
 	ext4 {
 		label = "rootfs"
+		use-mke2fs = true
 	}
 	size = 768M
 }

device/milkv-duos-musl-riscv64-sd/genimage.cfg

@@ -12,6 +12,7 @@ image boot.vfat {
 image rootfs.ext4 {
 	ext4 {
 		label = "rootfs"
+		use-mke2fs = true
 	}
 	size = 768M
 }