coresight: change flush input from pre_ares to flush_etr

Change flush input signal from pre_ares to flush_etr. For ETF
to be consistent with the usage model for both ETF and ETR.
Remove property reset-flush-race which is a workaround for
MSM8974v1.

Change-Id: I077f5215e75024e484abb3b68d67372ae6ccd154
Signed-off-by: Xiaogang Cui <xiaogang@codeaurora.org>