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/[email protected]
Signed-off-by: Colin Ian King <[email protected]>
Cc: Christophe JAILLET <[email protected]>
Cc: Sven Schmidt <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Joe Perches <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>