MIPS: JZ4740: use Ingenic SoC UART driver

Remove the serial support from arch/mips/jz4740 & make use of the new
Ingenic SoC UART driver. This is done for both regular & early console
output.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Kumar Gala <galak@codeaurora.org>
Cc: Lars-Peter Clausen <lars@metafoo.de>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: devicetree@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Stephen Warren <swarren@wwwdotorg.org>
Cc: linux-kernel@vger.kernel.org
Cc: Brian Norris <computersforpeace@gmail.com>
Cc: Apelete Seketeli <apelete@seketeli.net>
Cc: Alexandre Courbot <gnurou@gmail.com>
Patchwork: https://patchwork.linux-mips.org/patch/10160/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>