dt-bindings: clock: Add sc8280xp to the RPMh clock controller binding

The Qualcomm SC8280XP has a RPMh clock controller, so add a compatible
for this to the binding.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Stephen Boyd <sboyd@kernel.org>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20220223044516.3776637-1-bjorn.andersson@linaro.org