mkfs.ubifs: Add ZSTD compression

mkfs.ubifs: Add ZSTD compression

I added ZSTD support to mkfs.ubifs and compared the ZSTD results with
zlib/lzo and the available ZSTD compression levels. The results are in
the following table:

Comp    image MiB        time  image2 MiB        time
none          271   0m 0,723s         223   0m 0,589s
lzo           164   0m13,705s         116   0m11,636s
zlib          150   0m 7,654s         103   0m 6,347s
favor-lzo     158   0m21,137s         110   0m17,764s
zstd-01       154   0m 1,607s         106   0m 1,429s
zstd-02       153   0m 1,704s         105   0m 1,479s
zstd-03*      152   0m 1,888s         104   0m 1,668s
zstd-04       151   0m 2,741s         103   0m 2,391s
zstd-05       150   0m 3,257s         102   0m 2,916s
zstd-06       150   0m 3,735s         102   0m 3,356s
zstd-07       150   0m 4,066s         102   0m 3,705s
zstd-08       152   0m 1,857s         104   0m 1,644s
zstd-09       152   0m 1,855s         104   0m 1,639s
zstd-10       150   0m 6,654s         102   0m 6,195s
zstd-11       150   0m10,027s         102   0m 9,130s
zstd-12       149   0m14,724s         101   0m13,415s
zstd-13       148   0m18,232s         100   0m16,719s
zstd-14       148   0m20,859s         100   0m19,554s
zstd-15       148   0m25,033s         100   0m23,186s
zstd-16       148   0m38,837s         100   0m36,543s
zstd-17       148   0m46,051s         100   0m43,120s
zstd-18       148   0m49,157s         100   0m45,807s
zstd-19       148   0m49,421s         100   0m45,951s
zstd-20       148   0m51,271s         100   0m48,030s
zstd-21       148   0m51,015s         100   0m48,676s
zstd-22       148   0m52,575s         100   0m50,013s

The UBIFS image was created via
  mkfs.ubifs -x $Comp -m 512 -e 128KiB -c 2200 -r $image $out

I used "debootstrap sid" to create a basic RFS and the results are in
the `image' column. The image2 column denotes the results for the same
image but with .deb files removed.
The time column contains the output of the run time of the command.

ZSTD's compression level three is currently default. Based on the
compression results (for the default level) it outperforms LZO in
run time and compression and is almost as good as ZLIB in terms of
compression but quicker.
The higher compression levels make almost no difference in compression
but take a lot of time.

The compression level used is the default offered by ZSTD. It does not
make sense the higher levels.

Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>