Fix issues with oversized inputs in CAST and TABLE

CAST was not truncating values when downcasting integers, and table was
silently allowing values outsides of the input range when that should be
taken as an internal reference model error.

Add unit tests for CAST checking that the reference model has the proper
truncation behaviour.

Signed-off-by: Ian Tayler Lessa <ian.taylerlessa@arm.com>
Change-Id: If86068304a97c6bdbb7aacac33ef889cc2751c80