arm64: dts: qcom: sdm845-db845c: Mark cont splash memory region as reserved

arm64: dts: qcom: sdm845-db845c: Mark cont splash memory region as reserved

Adding a reserved memory region for the framebuffer memory
(the splash memory region set up by the bootloader).

It fixes a kernel panic (arm-smmu: Unhandled context fault
at this particular memory region) reported on DB845c running
v5.10.y.

Cc: stable@vger.kernel.org # v5.10+
Reviewed-by: Caleb Connolly <caleb.connolly@linaro.org>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230726132719.2117369-2-amit.pundir@linaro.org
Signed-off-by: Bjorn Andersson <andersson@kernel.org>