dt-bindings: remoteproc: qcom: wcnss: Add qcom,pronto compatible

This is not a fallback compatible, it must be present in addition to
"qcom,pronto-v*". It is also not documented in qcom,wcnss-pil.txt.  This
is the reason for documenting it in a separate commit.

This compatible is used in the wcn36xx driver to determine which
register must be accessed. However it isn't immediately clear why the
wcn36xx driver relies on this extra compatible string rather than just
looking for "qcom,pronto-v*".

Signed-off-by: Sireesh Kodali <sireeshkodali1@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221001031345.31293-4-sireeshkodali1@gmail.com