ARM: dts: msm: Reduce L2 dump size to 3 MB for fsm9900

Current memory map for FSM9900 targets allow only 3MB
for dump area.

Change-Id: Ic80544b88e8ecbc88e273726e369234a81250df4
Acked-by: Kaushik Sikdar <ksikdar@qti.qualcomm.com>
Signed-off-by: Rohit Vaswani <rvaswani@codeaurora.org>