ARM: dts: msm: reserve memory for display ramdump for sdmmagpie

Reserve memory for display ramdump feature on sdmmagpie target.
This memory buffer would be configured by the bootloader and
needs to be retained forever.

Change-Id: Ib3dc76f39141199d68874c8b334b791ee86bc8eb
Signed-off-by: Jayant Shekhar <jshekhar@codeaurora.org>