cmd: sata: Add block unbind device function

If we didn't unbind the sata from block device, the same devices would
be added after sata remove,
This patch is to resolve this issue as below:

=> sata info
SATA#0:
	(3.0 Gbps)
SATA#1:
	(3.0 Gbps)
Device 0: Model: INTEL SSDSA2BW300G3D Firm: 4PC10362 Ser#: BTPR247005PY30
            Type: Hard Disk
            Supports 48-bit addressing
            Capacity: 286168.1 MB = 279.4 GB (586072368 x 512)
Device 1: Model: INTEL SSDSA2BW300G3D Firm: 4PC10362 Ser#: BTPR247005VX30
            Type: Hard Disk
            Supports 48-bit addressing
            Capacity: 286168.1 MB = 279.4 GB (586072368 x 512)
=> sata stop
=> sata info
SATA#0:
	(3.0 Gbps)
SATA#1:
	(3.0 Gbps)
Device 0: Model: INTEL SSDSA2BW300G3D Firm: 4PC10362 Ser#: BTPR247005PY300
            Type: Hard Disk
            Supports 48-bit addressing
            Capacity: 286168.1 MB = 279.4 GB (586072368 x 512)
Device 1: Model: INTEL SSDSA2BW300G3D Firm: 4PC10362 Ser#: BTPR247005VX300
            Type: Hard Disk
            Supports 48-bit addressing
            Capacity: 286168.1 MB = 279.4 GB (586072368 x 512)
Device 2: Model: INTEL SSDSA2BW300G3D Firm: 4PC10362 Ser#: BTPR247005PY300
            Type: Hard Disk
            Supports 48-bit addressing
            Capacity: 286168.1 MB = 279.4 GB (586072368 x 512)
Device 3: Model: INTEL SSDSA2BW300G3D Firm: 4PC10362 Ser#: BTPR247005VX300
            Type: Hard Disk
            Supports 48-bit addressing
            Capacity: 286168.1 MB = 279.4 GB (586072368 x 512)

Signed-off-by: Peng Ma <peng.ma@nxp.com>
Reviewed-by: Simon Glass <sjg@chromium.org>