hw/ufs: Modify lu.c to share codes with SCSI subsystem

This patch removes the code that ufs-lu was duplicating from
scsi-hd and allows them to share code.

It makes ufs-lu have a virtual scsi-bus and scsi-hd internally.
This allows scsi related commands to be passed thorugh to the scsi-hd.
The query request and nop command work the same as the existing logic.

Well-known lus do not have a virtual scsi-bus and scsi-hd, and
handle the necessary scsi commands by emulating them directly.

Signed-off-by: Jeuk Kim <jeuk20.kim@samsung.com>