Clamp inverse transform coefficients

When --enable-coefficient-range-checking isn't specified,
clamp the coefficient at each stage.

The decoder behaviour is unchanged for valid existing AV1 streams.
However, some AV1 bitstreams that would have been rejected by the
decoder as illegal (range check failure) are now legal bitstreams.

There is no impact on video quality for valid bitstreams,
only bitstreams that would have been considered invalid are affected,
and are now considered as valid ones.

BUG=aomedia:30

Change-Id: Ie72ceeb3cb0561e8d3259767b209a4ef3be90438