Disable 32-bit PIO for 6Gbit/s Intel SATA controllers.

For some reason 32-bit PIO writes are not working on 6Gbit/s Intel SATA
ports, while 16/32-bit PIO reads and 16-bit PIO writes are working fine.
3Gbit/s ports on the same controllers have no this problem.

Workaround this by disabling 32-bit PIO for all Intel controllers that may
have 6Gbit/s ports. It halves PIO performance from 6MB/s to 3MB/s, but
who bother about speed of such rare and slow mode, which is also highly
discouraged by SATA specifications?

MFC after: 2 weeks