dt-bindings: arm: qcom: Document X1E80100 SoC and boards

Document the X1E80100 SoC binding and also the boards using it.
Also document the new board id qcp (Qualcomm Compute Platform).

Signed-off-by: Rajendra Nayak <quic_rjendra@quicinc.com>
Co-developed-by: Sibi Sankar <quic_sibis@quicinc.com>
Signed-off-by: Sibi Sankar <quic_sibis@quicinc.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>