h8300-elf port: gas patches

[Joern Rennecke]

> Err, no.  Keep all the existing tests which can be shared in h8300.exp.  Then

I did.

> create h8300-coff.exp and h8300-elf.exp for those which can not be shared.
> If you look at h8300-coff.exp you clearly didn't do that.  You'll find stuff
> like arithmetic, logical, bit, etc tests instead of just the branching
> tests.

I only ran the specific tests, but you are right in that I've left a lot
of support procedures that are not needed.  I've fixed this now.