Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Separate mse driver into a core driver and a bus attachments. Separate out
the ISA and CBUS (called isa on pc98) attachments. Eliminate all PC98
ifdefs in the process (the driver in pc98/pc98/mse.c was a copy of the one
in i386/isa/mse.c with PC98 ifdefs). Create a module for this driver.

I've tested this my PC-9821RaS40 with moused. I've not tested this on i386
because I have no InPort cards, or similar such things. NEC standardized
on bus mice very early, long before ps/2 mice ports apeared, so all PC-98
machines supported by FreeBSD/pc98 have bus mice, I believe.

Reviewed by: nyan-san