lib/lz4: make arrays static const, reduces object code size

lib/lz4: make arrays static const, reduces object code size

Don't populate the read-only arrays dec32table and dec64table on the
stack, instead make them both static const.  Makes the object code
smaller by over 10K bytes:

  Before:
     text	   data	    bss	    dec	    hex	filename
    31500	      0	      0	  31500	   7b0c	lib/lz4/lz4_decompress.o

  After:
     text	   data	    bss	    dec	    hex	filename
    20237	    176	      0	  20413	   4fbd	lib/lz4/lz4_decompress.o

(gcc version 7.2.0 x86_64)

Link: http://lkml.kernel.org/r/20170921221939.20820-1-colin.king@canonical.com
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Cc: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Cc: Sven Schmidt <4sschmid@informatik.uni-hamburg.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>