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

media/libstagefright/codecs/aacenc/Android.bp

@@ -55,7 +55,7 @@ cc_library_static {
 
             instruction_set: "arm",
 
-            armv7_a_neon: {
+            neon: {
                 exclude_srcs: [
                     "src/asm/ARMV5E/PrePostMDCT_v5.s",
                     "src/asm/ARMV5E/R4R8First_v5.s",

media/libstagefright/codecs/amrwbenc/Android.bp

@@ -75,7 +75,7 @@ cc_library_static {
 
             instruction_set: "arm",
 
-            armv7_a_neon: {
+            neon: {
                 exclude_srcs: [
                     "src/asm/ARMV5E/convolve_opt.s",
                     "src/asm/ARMV5E/cor_h_vec_opt.s",

media/libstagefright/codecs/on2/h264dec/Android.bp

@@ -35,7 +35,7 @@ cc_library_shared {
         arm: {
             instruction_set: "arm",
 
-            armv7_a_neon: {
+            neon: {
                 cflags: [
                     "-DH264DEC_NEON",
                     "-DH264DEC_OMXDL",