scsi: hisi_sas: Fix for setting the PHY linkrate when disconnected

scsi: hisi_sas: Fix for setting the PHY linkrate when disconnected

In commit 5ddfbd79e584 ("scsi: hisi_sas: Set PHY linkrate when
disconnected"), we use the sas_phy_data.enable flag to track whether the
PHY was enabled or not, so that we know if we should set the PHY negotiated
linkrate at SAS_LINK_RATE_UNKNOWN or SAS_PHY_DISABLED.

However, it is not proper to use sas_phy_data.enable, since it is only set
when libsas attempts to set the PHY disabled/enabled; hence, it may not
even have an initial value.

As a solution to this problem, introduce hisi_sas_phy.enable to track
whether the PHY is enabled or not, so that we can set the negotiated
linkrate properly when the PHY comes down.

Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>