Build support for 32-bit armv8-a

Since both armv7-a-neon and 32-bit armv8-a have NEON, we can treat them
the same in Android.bp.

Bug: 62895439
Test: Built modified aosp_arm64 with armv8-a as its TARGET_2ND_CPU_ARCH
      successfully.

Change-Id: Ib6db0c1515b0b59d76b2a3a2798cc12a7eea5914
diff --git a/Android.bp b/Android.bp
index a581b0a..7082f0b 100644
--- a/Android.bp
+++ b/Android.bp
@@ -695,7 +695,7 @@
                 "src/opts/SkBlitRow_opts_arm.cpp",
             ],
 
-            armv7_a_neon: {
+            neon: {
                 srcs: [
                     "src/opts/SkBitmapProcState_arm_neon.cpp",
                     "src/opts/SkBitmapProcState_matrixProcs_neon.cpp",