Fix encoder partitioned output on ARM

Fix encoder partitioned output on ARM

API was not returning correct partition sizes on arm targets.
The armv5 token packing functions were not storing the information to the
partition size table.
As a fix, have one boolcoder instance allocated for each partition so
that partition sizes are internally available after all partitions
were encoded. This will also allow more flexibility in producing
several partitions in parallel.

Use buffer validation (overflow check) in all ARM bitpacking
functions.

Change-Id: I31c8a11d8a7613676f0ff50928cb2a2ab14fd169