fdc: add CCR (Configuration Control Register) write register

DIR and CCR registers share the same address ; DIR is read-only
while CCR is write-only

CCR register is used to change media transfer rate, which will be
checked in following changes.

Signed-off-by: Hervé Poussineau <hpoussin@reactos.org>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
