dt-bindings: soc: qcom: Add bindings for Qualcomm Ramp Controller

Document the Qualcomm Ramp Controller, found on various legacy
Qualcomm SoCs.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221117132956.169432-2-angelogioacchino.delregno@collabora.com