ARM: dts: msm: add sg-enable to tmc etr dt node for msmtellurium

Add sg-enable to TMC-ETR DT node to indicate that scatter gather
feature is supported with TMC-ETR configuration. The sg-enable DT
entry will help enable this feature only on those targets which
support it.

Change-Id: I0786c83a633908aabfcf45457b9dcb10d09a4095
Signed-off-by: Xiaogang Cui <xiaogang@codeaurora.org>