Staging: ti-st: give proto drivers context

protocol drivers such as BT, FM and GPS when registering
to ST now provide their own private data which they expect
when their functions namely registration completed & receive
are called.
Also upon tty_close, set protos_registered count to 0, although
all protocols are marked un-registered.

Signed-off-by: Pavan Savoy <pavan_savoy@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>