dt-bindings: net: qcom,ipa: add support for SM8350

Add support for "qcom,sm8350-ipa", which uses IPA v4.9.

Use "enum" rather than "oneOf/const ..." to specify compatible
strings, as suggested by Rob Herring.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>