defconfig: msm: disable serial console in perf defconfig

Serial console increases suspend/resume latencies and impacts
system power. So disabling it by default in perf defconfig.

Change-Id: I69a9fa3a631f2e89ba53b181d76e6cf1f298311a
Signed-off-by: Sravan Kumar Ambapuram <asravan@codeaurora.org>