Android: support AArch-64

[carstene1ns]

My tablet uses this 😁. ABI is arm64-v8a.

[Ghabry]

Soon we reach the APK size limit :D

[Ghabry]

Google requires this by 2019, so we should slowly add it ;)

Due to a bug in binutils, NDK it should be updated to r16 first because it might generate broken binaries in previous versions, however this requires to update the build script to use unified headers.
r16 still supports armeabi, mips and mips64 targets, but deprecated.

[carstene1ns]

Okay, so time to drop mips support ~~~~

(from https://android.jlelse.eu/controlling-apk-size-when-using-native-libraries-45c6c0e5b70a)