AM33: adding some more register classes

[Alexandre Oliva]

I won't pretend to be able to explain why adding the classes AM33_REGS
and SP_OR_AM33_REGS makes any difference, given that they're just
duplicates of GENERAL_REGS and ALL_REGS, but the fact is that they do
:-)

v mn10300-elf/am33/libio/libio.a 23726 23725
v mn10300-elf/am33/libio/libiostream.a 64988 64987
v mn10300-elf/am33/libstdc++/libstdc++.a 70826 70825
v mn10300-elf/libio/libiostream.a 63662 63643
v mn10300-elf/libstdc++/libstdc++.a 69460 69441

Ok to install?