devicetree: bindings: Update qcom,saw2 node bindings

Update qcom,saw2 node bindings with compatible strings to identify nodes
that provides cpuidle functionality for a particular SoC. Remove
unused compatible strings.

Update examples for different SAW nodes.

Signed-off-by: Lina Iyer <lina.iyer@linaro.org>
Signed-off-by: Kumar Gala <galak@codeaurora.org>
Signed-off-by: Olof Johansson <olof@lixom.net>