drm/i915/gvt: Constify formats

These are never modified, so make them const to allow the compiler to
put them in read-only memory. WHile at it, make the description const
char* since it is never modified.

Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Signed-off-by: Zhi Wang <zhi.a.wang@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20211204105527.15741-8-rikard.falkeborn@gmail.com


Reviewed-by: Zhi Wang <zhi.a.wang@intel.com>