New unified powerpc majors file

I have created a new unified majors file for the powerpc ports to share.  This
majors file was based on the majors file from macppc.  Ports can switch to this
file by performing the following steps:

1) delete conf/majors.port
2) edit conf/files.port to point to "arch/powerpc/conf/majors.powerpc"
3) copy etc/etc.ofppc/MAKEDEV.conf to your etc/etc.port directory
4) test MAKEDEV.  If you get complaints about unknown devices, you can delete
those items from your MAKEDEV.conf file.

Notes on this new majors file:

macppc and sandpoint should be fully compatible with this majors file, so there
is no reason those two ports couldn't switch immediately.

evbppc is mostly compatible, the gtmpsc device had to be moved, but that is
only used by the ev64260 port.. so it probably woudln't affect many users.

ofppc has already switched.

As for other ports, such as mvmeppc, bebox, etc.  This new majors file is not
compatible with your old majors.  However, some of these ports have not really
had a viable release in a long time, and likely have no users.  I'd like to see
as many ports as possible switch over to it, as long as the portmasters think
the impact will be low.  I think that for mvmeppc and bebox, the impact would
be pretty small.  I don't know how many users ibmnws really has...

(I'm still debating this on prep, as prep has users, and the change is pretty
significant to prep)