Remove EISA bus support for add-in cards. Remove related kernel and
compile options. Remove doxygen pointers to now deleted files. Remove
EISA and VME as examples in bus_space.9.

Retained EISA mode code for IO PIC and MPTABLES because that's not
EISA bus, per se, and some people have abused EISA to mean "EISA-like
behavior as opposed to ISA" rather than using it for EISA add-in
cards.

Relnotes: yes