ARM: mxs: dts: Enable DCP for MXS

Enable the DCP by default on both i.MX23 and i.MX28.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: David S. Miller <davem@davemloft.net>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Shawn Guo <shawn.guo@linaro.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>