dt-bindings: soc: qcom: smd-rpm: Fix missing MSM8936 compatible

Add compatible msm8936. msm8936 covers both msm8936 and msm8939.
The relevant driver already has the compat string but, we haven't
documented it.

Fixes: d6e52482

 ("drivers: soc: Add MSM8936 SMD RPM compatible")
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220418231857.3061053-1-bryan.odonoghue@linaro.org