dt-bindings: PCI: qcom: Add SA8540P to binding

SA8540P is a new platform related to SC8280XP but which uses a single
host interrupt for MSI routing.

Link: https://lore.kernel.org/r/20220714071348.6792-4-johan+linaro@kernel.org


Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Reviewed-by: Brian Masney <bmasney@redhat.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Stanimir Varbanov <svarbanov@mm-sol.com>