Add detailed AC_ERR_* flags and use them.  Long-term goal is to
describe all errors with err_mask and tf combination (tf for failed
sector information, etc...).  After proper error diagnosis is
implemented, sense data should also be generated from err_mask instead
of directly from hardware tf registers as it is currently.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>