Adding Internal Input Buffer

Allocating a input buffer in the decoder context and copying all input
to this buffer before using. This will ensure that we do not access
memory out of bounds because of our bit read optimisations.

Change-Id: I0a76365387822267508cd5804bc7c34bc0ba23cb
Author: Venkatarama NG. Avadhani <venkatarama.avadhani@ittiam.com>
Date:   Thu Feb 15 09:33:38 2018 +0530
Bug: 72764648
Test: poc before/after
Merged-In: Ide6c58291fa1d0472a9589c95aba231d13122a19