ARM: dts: msm: reserve splash memory for HDMI display on 8996

The splash screen for HDMI as primary utilizes a piece of memory
to hold and subsequently display the splash logo while in the
bootloader. We need to reserve the same splash memory buffer
in order to support continuous splash screen on msm8996 target,
when the device is booting into the kernel. This memory is
cleaned up later once display driver hand-off is completed
and the framework has booted up.

Change-Id: I59a5dcf05ef0effcf31cb03979c4464394d68896
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>