ARM: dts: msm: reduce tmc etr ddr buffer size

Ram dump parser takes longer for parsing 32M ETR DDR buffer
with TMC configuration. Reduce the ETR DDR buffer size to 4M.

Change-Id: I1baefdbac5d80bbe87e5c23e42502342dd474845
Signed-off-by: Sarangdhar Joshi <spjoshi@codeaurora.org>