video: fbdev: fsl-diu-fb: constify mfb_template and fsl_diu_match.

File size before:
   text	   data	    bss	    dec	    hex	filename
   2469	   1552	     24	   4045	    fcd	drivers/video/fbdev/fsl-diu-fb.o

File size after adding 'const':
   text	   data	    bss	    dec	    hex	filename
   3821	    200	     24	   4045	    fcd	drivers/video/fbdev/fsl-diu-fb.o

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Cc: Timur Tabi <timur@tabi.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>