zram: add dictionary support to lz4

zram: add dictionary support to lz4

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

TEST
====
*** lz4
/sys/block/zram0/mm_stat
1750654976 664188565 676864000        0 676864000        1        0    34288    34288

*** lz4 dict=/home/ss/lz4-dict-amd64
/sys/block/zram0/mm_stat
1750638592 619891141 632053760        0 632053760        1        0    34278    34278

*** lz4 level=5 dict=/home/ss/lz4-dict-amd64
/sys/block/zram0/mm_stat
1750638592 727174243 740810752        0 740810752        1        0    34437    34437

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

Link: https://lkml.kernel.org/r/20240712051850.484318-21-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>