Moves error concealment allocations from common parts to decoder

The backup MODE_INFO buffer used in the error concealment was
allocated in the codec common parts allocation even though this is a
decoder only resource. Moved the allocation to the decoder side.
No need to update_mode_info_border as mode_info buffers are zero
allocated.

This fixes also a potential memory leak as the EC overlaps buffer was not
properly released before reallocation after a frame size change.

Change-Id: I12803d3e012308d95669069980b1c95973fb775f