Merge the PC98 fdc(4) driver into the MI driver.  While here, replace
the magic numbers used with NE7CMD_SPECIFY with invocations of the
NE7_SPEC_x() macros.

Approved by:	nyan


git-svn-id: svn+ssh://svn.freebsd.org/base/head@272129 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f