Bluetooth-OPP: Monitor display status during transfer

Check the status of the display during ongoing transfer to avoid
creating new update threads for updating the transfer progress if
display is off. Otherwise, power consumption will increase even
though display is off because of starting new thread every one
second.

CRs-Fixed: 745331
Change-Id: I862a163d31cf9a174e907ccb48b92e7cf77b4441