Provide a more consistent output of the encoded instruction

Created by: jeremybennett

The encoded instruction hex was being dumped to the assembly file
in minimal length, making it hard to read when and encoding has
leading zeros. This is a partial fix, which prints all decodes as
32-bit width.

However the architecture should be interrogated to ask what
instruction length should be used, and the field padded as
necessary with blanks. This will be needed for correct binary
representation of architectures with variable length instructions,
or fixed instruction length other than 32.

Files changed:

* base/src/TestIO.cc (TestImage::DumpToAssembly): Force output of
the opcode hex representation to be 8 hex digits long.

Signed-off-by: Jeremy Bennett jeremy.bennett@embecosm.com