FDC fix 5/10 (Hervé Poussineau):
- Better handling of DOR register. DOR register drives external motors, but it not limited to existing drives.
- Use FD_DOR_nRESET flag instead of internal FD_CTRL_RESET flag.
- Support writing to DOR register even in reset mode (as said in specification)


git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@4285 c046a42c-6fe2-441c-8c8c-71466251a162
