clk: vc5: Add bindings for IDT VersaClock 5P49V5935

IDT VersaClock 5 5P49V5935 has 4 clock outputs, 4 fractional dividers.
Input clock source can be taken from either integrated crystal or from
external reference clock.

Signed-off-by: Alexey Firago <alexey_firago@mentor.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>