usb/uas: use unique tags for all LUNs

I observed that on a device with multiple LUNs UAS was re-using the same
tag number for requests which were issued at the same time to both LUNs.
This patch uses scsi_init_shared_tag_map() to use unique tags for all
LUNs. With this patch I haven't seen the same tag number during the init
sequence anymore. Tag 1 is used for devices which do not adverise
command queueing.
This patch initilizes the queue before adding the scsi host like the
other two user in tree.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>