Enable 32-bit armv8 NEON for aac/amrwb/h264 codecs

Since ARM neon instructions were only used on armv7-a-neon
architecture variant, the default implementations for these
codecs don't use these advanced SIMD instructions.

Bug: 65568372
Test: lunch aosp_arm64; emulator # on oc-mr1-dev; boot to home screen
      Check neon code is included in the following libraries:
      - libstagefright_aaeenc.a
      - libstagefright_amrwbenc.a
      - libstagefright_soft_h264dec.so
Change-Id: Ia7a6097425541cb59fc470eac04e9c935be88325