AmrnbEncoderTest: Added AndroidTest.xml to run test with atest

<?xml version="1.0" encoding="utf-8"?>

<!-- Copyright (C) 2020 The Android Open Source Project

     Licensed under the Apache License, Version 2.0 (the "License");

     you may not use this file except in compliance with the License.

     You may obtain a copy of the License at

          http://www.apache.org/licenses/LICENSE-2.0

     Unless required by applicable law or agreed to in writing, software

     distributed under the License is distributed on an "AS IS" BASIS,

     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

     See the License for the specific language governing permissions and

     limitations under the License.

-->

<configuration description="Test module config for Amr-nb Encoder unit test">

    <option name="test-suite-tag" value="AmrnbEncoderTest" />

    <target_preparer class="com.android.tradefed.targetprep.PushFilePreparer">

        <option name="cleanup" value="true" />

        <option name="push" value="AmrnbEncoderTest->/data/local/tmp/AmrnbEncoderTest" />

        <option name="push-file"

            key="https://storage.googleapis.com/android_media/frameworks/av/media/libstagefright/codecs/amrnb/enc/test/AmrnbEncoderTest.zip?unzip=true"

            value="/data/local/tmp/AmrnbEncoderTestRes/" />

    </target_preparer>

    <test class="com.android.tradefed.testtype.GTest" >

        <option name="native-test-device-path" value="/data/local/tmp" />

        <option name="module-name" value="AmrnbEncoderTest" />

        <option name="native-test-flag" value="-P /data/local/tmp/AmrnbEncoderTestRes/" />

    </test>

</configuration>

adb push ${OUT}/data/nativetest/AmrnbEncoderTest/AmrnbEncoderTest /data/local/tmp/

```

The resource file for the tests is taken from [here](https://drive.google.com/drive/folders/13cM4tAaVFrmr-zGFqaAzFBbKs75pnm9b). Push these files into device for testing.

Download amr-nb_encoder folder and push all the files in this folder to /data/local/tmp/ on the device.

The resource file for the tests is taken from [here](https://storage.googleapis.com/android_media/frameworks/av/media/libstagefright/codecs/amrnb/enc/test/AmrnbEncoderTest.zip). Download, unzip and push these files into device for testing.

```

adb push amr-nb_encoder/. /data/local/tmp/

adb push AmrnbEncoderTestRes/. /data/local/tmp/

```

usage: AmrnbEncoderTest -P \<path_to_folder\>

```

adb shell /data/local/tmp/AmrnbEncoderTest -P /data/local/tmp/

adb shell /data/local/tmp/AmrnbEncoderTest -P /data/local/tmp/AmrnbEncoderTestRes/

```

Alternatively, the test can also be run using atest command.

```

atest AmrnbEncoderTest -- --enable-module-dynamic-download=true

```