dt-bindings: arm: qcom: Document sdm632 and fairphone,fp3 board

Add binding documentation for Fairphone 3 smartphone which is based on
Snapdragon 632 (sm632).

Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220220201909.445468-10-luca@z3ntu.xyz