[SCSI] sd: pause in sd_spinup_disk for slow USB devices

This patch adds a delay tailored for USB flash devices that are slow to
initialize their firmware.  The symptom is a repeated Unit Attention with
ASC=0x28 (Not Ready to Ready transition).  The patch will wait for up to 5
seconds for such devices to become ready.  Normal devices won't send the
repeated Unit Attention sense key and hence won't trigger the patch.

This fixes a problem with James Roberts-Thomson's USB device, and I've
seen several reports of other devices exhibiting the same symptoms --
presumably they will be helped as well.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>