dt-bindings: arm: qcom: separate msm8996pro bindings

Xiaomi Mi 5s Plus (natrium) and Xiaomi Mi Note 2 (scorpio) use
MSM8996Pro rather than plain MSM8996. Describe this in the arm/qcom.yaml
bindings.

Since MSM8996Pro is largely compatible with MSM8996, keep old compatible
too rather than insiting on qcom,msm8996pro only. This allows the code
that doesn't yet know about msm8996pro to continue supporting these
devices.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20220724140421.1933004-2-dmitry.baryshkov@linaro.org