MIPS: DTS: jz4740: Add node for the MMC driver

Add a devicetree node for the jz4740-mmc driver.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: devicetree@vger.kernel.org
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-mmc@vger.kernel.org