dt-bindings: clock: add clock definitions for Ralink SoCs

Add clock missing definitions for RT2880, RT305X, RT3352, RT3383, RT5350,
MT7620 and MT76X8 Ralink SoCs. Update bindings to clarify clock depending
on these new introduced constants so consumer nodes can easily use the
correct one in DTS files matching properly what is being used in driver
code (clock IDs are implicitly used there).

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>