ARM: dts: msm: add dummy SPSS ETM device for SDM845

Add dummy device for SPSS ETM. This device can be used to configure
SPSS ETM trace path.

Change-Id: I63d269940dbb68d8beb5549914b221b4b1b65979
Signed-off-by: Satyajit Desai <sadesai@codeaurora.org>