drm: armada: Constify drm_prop_enum_list structures.

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

File size before:
text data bss dec hex filename
3594 176 0 3770 eba drivers/gpu/drm/armada/armada_overlay.o

File size After adding 'const':
text data bss dec hex filename
3722 48 0 3770 eba drivers/gpu/drm/armada/armada_overlay.o

Signed-off-by: Arvind Yadav <[e-mail]>
Signed-off-by: Daniel Vetter <[e-mail]>
Link: http://patchwork.freedesktop.org/patch/msgid/dbeb176[e-mail]

drivers/gpu/drm/armada/armada_overlay.c

···
 	DRM_FORMAT_BGR565,
 };
 
-static struct drm_prop_enum_list armada_drm_colorkey_enum_list[] = {
+static const struct drm_prop_enum_list armada_drm_colorkey_enum_list[] = {
 	{ CKMODE_DISABLE, "disabled" },
 	{ CKMODE_Y,       "Y component" },
 	{ CKMODE_U,       "U component" },