drm/i915/ehl: Add missing VECS engine

EHL can have up to one VECS(video enhancement) engine, so add it to
the device_info.

BSpec: 29152
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Bob Paauwe <bob.j.paauwe@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Clint Taylor <Clinton.A.Taylor@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190614213749.15870-1-jose.souza@intel.com