scsi: ufs: Protect PM ops and err_handler from user access through sysfs

User layer may access sysfs nodes when system PM ops or error handling is
running. This can cause various problems. Rename eh_sem to host_sem and use
it to protect PM ops and error handling from user layer intervention.

Link: https://lore.kernel.org/r/1610594010-7254-3-git-send-email-cang@codeaurora.org
Reviewed-by: Stanley Chu <stanley.chu@mediatek.com>
Acked-by: Avri Altman <avri.altman@wdc.com>
Signed-off-by: Can Guo <cang@codeaurora.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>