arm64: dts: qcom: sdm630-nile: Reserve simplefb memory

Reserve the bit of memory that simplefb uses to ensure it can always
probe.

Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230116141451.470158-2-konrad.dybcio@linaro.org