xtensa: 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.

Move of_clk_init() into time_init(), then drop xtensa_device_probe() fully.

Cc: Chris Zankel <chris@zankel.net>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Rob Herring <robh@kernel.org>