Increase min input buffer size for video decoders to 2 MB

In some cases, applications send wrong max-width and max-height,
which results in a smaller than required input buffer.

Bug: 140780744
Test: verify max-input-size
Test: atest android.media.cts.DecoderTest

Change-Id: I9a16de4708cc38d32194a1c8b4666f7b1efd2d28