Do not use "Enable Implied Seek" on enhanced floppy controllers. This

Do not use "Enable Implied Seek" on enhanced floppy controllers.  This
breaks the "2step" feature of the driver, e.g. in order to read 360
KiB media on a 1200 KiB drive.

As the only potential advantage of implied (vs. explicit) seeks is to
minimize the software effort, yet our driver always contained the
logic needed for explicit seeks, simply dropping implied seeks is the
best solution without introducing risks for new bugs.  There is no
performance penalty, reading a 1440 KiB medium takes exactly the same
time with both, implied or explicit seeks.

MFC after:	1 week