dt-bindings: soc: qcom: qcom,pmic-glink: document QCM6490 compatible

Document the QCM6490 compatible used to describe the pmic glink on this
platform.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Luca Weiss <luca.weiss@fairphone.com>
Link: https://lore.kernel.org/r/20240208-fp5-pmic-glink-v2-1-4837d4abd5a4@fairphone.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>