drm: qxl: constify ttm_place structures.

drm: qxl: constify ttm_place structures.

ttm_place are not supposed to change at runtime. All functions
working with ttm_place provided by <drm/ttm/ttm_placement.h> work
with const ttm_place. So mark the non-const structs as const.

File size before:
   text	   data	    bss	    dec	    hex	filename
   3485	    184	    264	   3933	    f5d	drivers/gpu/drm/qxl/qxl_ttm.o

File size After adding 'const':
   text	   data	    bss	    dec	    hex	filename
   3501	    152	    264	   3917	    f4d	drivers/gpu/drm/qxl/qxl_ttm.o

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/a4f21d3bd2497129f084b8055ecf27f0d3ff1bba.1499013516.git.arvind.yadav.cs@gmail.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>