dt-bindings: mailbox: qcom-ipcc: document the support for SA8255p

Add a compatible for the ipcc on SA8255p platforms.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Nikunj Kela <quic_nkela@quicinc.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>