i965: Fix depth field setting in surface state for raw buffer on Gen7/8

i965: Fix depth field setting in surface state for raw buffer on Gen7/8

On Gen7/8 for RAW surface format, the depth field (surf[3]) in surface
state means [30:21] bits of number of entries which is different from
other surface format which uses [26:21] bits field.

Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>