spi: ti-qspi: one only one interrupt handler

The here used irq and threaded irq handler is a complete non-sense. After
the status register is read and the source disabled it schedules a thread
(the irq thread) to read the status from the variable, invoke complete()
and then renable the interrupt. Again: schedule a thread which invokes
_only_ complete().
This patch removes this non-sense and we remain with one handler which
invokes complete() if needed.
The device remove path should now disable the interupts.
This has been compile time tested.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Sourav Poddar <sourav.poddar@ti.com>
Signed-off-by: Mark Brown <broonie@linaro.org>