Add NEON intrinsics version for WebRtcSpl_MinValueW16Neon

WebRtcSpl_MinValueW16Neon is added. SplTest in common_audio_unittests
is passed on ARM32/ARM64 platforms.

BUG=4002
R=andrew@webrtc.org, jridges@masque.com

Change-Id: I33c3853766d7594ed121166288e5325a03b3d6fe

Review URL: https://webrtc-codereview.appspot.com/32639004

Patch from Yang Zhang <yang.zhang@arm.com>.

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7867 4adac7df-926f-26a2-2b94-8c16560cd09d