arm64: dts: qcom: ipq8074: add the reserved-memory node

On IPQ8074, 4MB of memory is needed for TZ. So mark that region
as reserved.

Signed-off-by: Kathiravan T <quic_kathirav@quicinc.com>
[bjorn: Squash with existing reserved-memory node]
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/1641560078-860-1-git-send-email-quic_kathirav@quicinc.com