clk: imx6q: optionally get CCM inputs via standard clock handles

clk: imx6q: optionally get CCM inputs via standard clock handles

When specifying external clock inputs to the CCM the current code
requires the clocks to be in a "clocks" child node of the DT root.
This is not really conformant with DT best practices.

To avoid the need to deviate from those best practices, allow the
clock inputs to be specified via standard clock handles. This is
in line with how drivers of the later CCM driver revisions on
newer i.MX SoCs handle this.

As we can't retroactively change the DT binding, allow this as an
option with a fallback to the old way of how this has been handled.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>