MIPS: Ci20: Enable RTC driver

Update the Ci20's defconfig to enable the JZ4780's RTC driver.

Signed-off-by: Mathieu Malaterre <malat@debian.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Paul Cercueil <paul@crapouillou.net>
Cc: Krzysztof Kozlowski <krzk@kernel.org>
Cc: devicetree@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/17236/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>