ARM: dts: msm: reserve memory for continuous splash pipeline for SDM845

Reserve memory for continuous splash feature on
SDM845 target. This memory buffer would be
configured by the bootloader and needs to be
retained until the first frame update in kernel.

Change-Id: I0f2bc8ad3c93b03de7c5be12f647aa495e4d1925
Signed-off-by: Shashank Babu Chinta Venkata <sbchin@codeaurora.org>