metag: Remove unnecessary of_platform_populate with default match table

After patch "of/platform: Add common method to populate default bus",
it is possible for arch code to remove unnecessary callers of
of_platform_populate with default match table.

Cc: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Rob Herring <robh@kernel.org>