drivers:misc: ti-st: set right debug levels for logs

pr_debug-ing few pr_infos from the data paths such as tty receive and
write so as to reduce debugs when we have higher logging levels enabled
undef VERBOSE in receive to avoid huge logs when log level 8 is set.

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