ARM: dts: msm: reserve cont-splash buffer memory

Reserve memory for continuous splash screen feature
to avoid any kernel module from overwriting it during
boot up. This memory will be released by MDSS driver
when it receives first update from surface flinger.

Change-Id: I8f53e12846df3f257dab56c34cf45aaea00db591
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>