mse reorg

[M. Warner Losh]

I've reorganized the mse driver.  I've split it up into cbus and isa
bus front ends, and a core back end and moved it to dev/mse.  I've
also made it into a module.

These patches eliminate all ifdefs in the driver by moving the machine
specific parts to the bus attachment front ends.  We can stop tracking
two copies in the tree (although it doesn't seem to be a huge burdon).

Please test this, especially on i386.  I've tested it on pc98 with
moused and it works the same as before as far as I can tell.

Why did I do this?  The PC-98 platform standardized on bus mice before
the ps/2 mouse standard evolved in the US.  I have a PC-98 machine
that I'd like to clean up a number of issues I promised to clean up a
long time ago.  On the road to doing that, I noticed that this driver
didn't support PNP on pc98, so I thought I'd add that (turns out that
the isa layer needs to change, and in turn shows that using isa for
both isa and cbus is flawed, but more about that later).  In adding
that, I thought it would be easy to eliminate the ifdefs, and this is
the result.

Comments?  Test results on i386?

Warner

	http://people.freebsd.org/~imp/mse.diff