c2SoftAmr: dont discard trailing samples during encoding

amr plugins at the point of eos, if they do not contain integral
multiple of frame size samples, they are discarding it. this change
aligns them to frame size by adding mute samples and encodes them

Bug: 375055097
Test: atest MctsMediaV2TestCases:AudioEncoderTest
Test: atest MctsMediaV2TestCases:CodecEncoderTest
Test: atest MctsMediaEncoderTestCases:EncoderTest
Test: atest MctsMediaV2TestCases:CodecEncoderBlockModelTest
Test: atest MctsMediaV2TestCases:CodecEncoderMultiAccessUnitTest
Test: atest MctsMediaV2TestCases:CodecEncoderBlockModelMultiAccessUnitTest
Test: atest VtsHalMediaC2V1_0TargetAudioEncTest

Change-Id: Icc354e258d5db0369d2957c1c186fbee62087df5