Revert "tty: serial: OMAP: transmit FIFO threshold interrupts don't wake the chip"

This reverts commit 43cf7c0bebf50d0b68aa42ae6d24cf08e3f24823 as Paul
wants to redo it.

Cc: Paul Walmsley <paul@pwsan.com>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Govindraj Raja <govindraj.r@ti.com>
Cc: Kevin Hilman <khilman@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>