ARM: dts: msm: increase fb mem sz for 1080p panel in samarium

Increase the amount of contiguous memory required by
the framebuffer device to accommodate the 1080p panel
used in msmsamarium boards to 24M. This adjustment is
needed to display with sw composition enabled.

Change-Id: I1b73ffe606c63f4ef935e958a46a3440d4195443
Signed-off-by: Manoj Rao <manojraj@codeaurora.org>