defconfig: msm: disable serial console in 8916 perf defconfig

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

Change-Id: I2480f33633521e10086accd6855c1eaf8d34cb70
Signed-off-by: Sravan Kumar Ambapuram <asravan@codeaurora.org>