zram: add dictionary support to lz4hc

zram: add dictionary support to lz4hc

Support pre-trained dictionary param. Just like lz4,
lz4hc doesn't mandate specific format of the dictionary
and zstd --train can be used to train a dictionary for
lz4, according to [1].

TEST
====

*** lz4hc
/sys/block/zram0/mm_stat
1750638592 608954620 621031424        0 621031424        1        0    34288    34288

*** lz4hc dict=/home/ss/lz4-dict-amd64
/sys/block/zram0/mm_stat
1750671360 505068582 514994176        0 514994176        1        0    34278    34278

[1] https://github.com/lz4/lz4/issues/557

Link: https://lkml.kernel.org/r/20240712051850.484318-22-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Nick Terrell <terrelln@fb.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>