Try to establish APM connection interface.

  * i386/Makefrag.am: Add apm target.
  * i386/configfrag.ac: Likewise.
  * i386/i368at/apm.c: APM driver.
  * i386/i386at/apm.h: APM driver header.
  * i386/i386at/model_dep.c: Init and establish APM driver in boot
                             sequence.