Remove EISA support from ahc driver. The AIC-7770 chip can be on ISA,
VesaLocalBus or EISA. Internally, EISA and ISA are handled the same,
with VL being handled slightly differently. To avoid too much code
churn, retain the EISA name, despite it being used only for ISA
bus. When it is on the ISA bus, weird gymnastics are required with
EISA-space address accesses as well. Remove known models from the ahc
man page. Remove ahc_eisa module.