ARM: imx6q: drop of_platform_default_populate() from init_machine

Dropping the machine_init specific of_platform_default_populate() can be
done safely due to the following two facts:

1)
Since commit 44a7185c

 ("of/platform: Add common method to populate
default bus") we have a common method to populate the devices.

2)
The machine_init code don't need bounded devices<>drivers since the code
uses syscon_regmap_lookup_by_compatible() which register a syscon
device on demand.

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>