dt: Add bindings for IDT VersaClock 5P49V5925

IDT VersaClock 5 5P49V5925 has 5 clock outputs, 4 fractional dividers.
Input clock source can be taken only from external reference clock.

Signed-off-by: Vladimir Barinov <vladimir.barinov+renesas@cogentembedded.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>