ARM: dts: msm: Increase the secure display heap size

Increase the secure_display_heap memory to support the
dual playback for sm6150 target.

Change-Id: I47094a6d79b4eadf12a309d2f2ffd1d99eecc7d3
Signed-off-by: Mohamed Sunfeer <msunfeer@codeaurora.org>