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

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: I08142f20d0c68c38a82d91b6b016f8ca06aaff84
Signed-off-by: Xiaogang Cui <xiaogang@codeaurora.org>