MIPS: lantiq: Use of_platform_default_populate instead of __dt_register_buses

MIPS: lantiq: Use of_platform_default_populate instead of __dt_register_buses

This allows populating syscon devices which are using "simple-mfd"
instead of "simple-bus".

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Cc: john@phrozen.org
Cc: robh@kernel.org
Cc: andy.shevchenko@gmail.com
Cc: p.zabel@pengutronix.de
Cc: kishon@ti.com
Cc: mark.rutland@arm.com
Cc: linux-mips@linux-mips.org
Cc: linux-mtd@lists.infradead.org
Cc: linux-watchdog@vger.kernel.org
Cc: devicetree@vger.kernel.org
Cc: linux-spi@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/17116/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>