arch: nios2: Enable the common clk subsystem on Nios2

This patch adds support for common clock framework on Nios2. Clock
framework is commonly used in many drivers, and this patch makes it
available for the entire architecture, not just on a per-driver basis.

Signed-off-by: Beniamin Bia <beniamin.bia@analog.com>
Signed-off-by: Dragos Bogdan <dragos.bogdan@analog.com>
Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>

nios2: 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: Ley Foon Tan <lftan@altera.com>
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Rob Herring <robh@kernel.org>

nios2: Device tree support

Add device tree support to arch/nios2.

Signed-off-by: Ley Foon Tan <lftan@altera.com>