The arch code calls of_platform_populate() with default match table
when it wants to populate default bus.

This patch introduce a new of_platform_default_populate_init() and make it
arch_initcall_sync(it should be later than some iommu configration, eg,
of_iommu_init() and swiotlb_late_init in arm64), then we can finish above
job in common method.

In order to avoid the default bus being populated twice, simply checking
the flag of bus node whether has be set OF_POPULATED_BUS or not.

After that, we can safely remove the caller in arch code.

Btw, add debug print in of_platform_populate(), and use __func__ to
print function's name of of_platform_bus_create().

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Frank Rowand <frowand.list@gmail.com>
Cc: Grant Likely <grant.likely@linaro.org>
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Rob Herring <robh@kernel.org>