Adding WebRtcSpl_MaxAbsValueW16 intrinsics version

The modification only uses the unique part of the WebRtcSpl_MaxAbsValue
 function. Pass Spltest.MinMaxOperationTest conformance test on both
 ARMv7 and ARM64. And the single function performance is similar with
 original assembly version on different platforms. If not specified, the
 code is compiled by GCC 4.6. The result is the "X version / C version"
 ratio, and the less is better.

| run 100k times             | cortex-a7 | cortex-a15 |
| use C as the base on each  |  (1.2Ghz) |   (1.7Ghz) |
| CPU target                 |           |            |
|----------------------------+-----------+------------|
| Neon asm                   |       32% |        15% |
| Neon intrinsics (GCC 4.6)  |       36% |        37% |
| Neon intrinsics (GCC 4.8)  |       35% |        18% |

BUG=3580
R=andrew@webrtc.org, jridges@masque.com

Change-Id: Ia2f6822ec58774b401cc440b6751a97e540b5048

Review URL: https://webrtc-codereview.appspot.com/30109004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7803 4adac7df-926f-26a2-2b94-8c16560cd09d