libata: separate ATA_EHI_DID_RESET into DID_SOFTRESET and DID_HARDRESET

Separate ATA_EHI_DID_RESET into ATA_EHI_DID_SOFTRESET and
ATA_EHI_DID_HARDRESET.  ATA_EHI_DID_RESET is redefined as OR of the
two flags.  This patch doesn't introduce any behavior change.  This
will be used later to determine whether _SDD is necessary or not.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>