ARM: dts: msm: reserve memory for continuous splash for sm8150

Reserve memory for continuous splash feature on
sm8150 target. This memory buffer would be
configured by the bootloader and needs to be
retained until the first frame update in the kernel.

Change-Id: Ibec432396f1da1780375b621bee39994152e8032
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>