openpic: fix CTPR and de-assertion of interrupts

Properly implement level-triggered interrupts by withdrawing an
interrupt from the raised queue if the interrupt source de-asserts.
Also withdraw from the raised queue if the interrupt becomes masked.

When CTPR is written, check whether we need to raise or lower the
interrupt output.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
