dt-bindings: clock: add dt binding header for mt7621 clocks

Adds dt binding header for 'mediatek,mt7621-clk' clocks.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20210309052226.29531-2-sergio.paracuellos@gmail.com


Signed-off-by: Stephen Boyd <sboyd@kernel.org>