gpu: nvgpu: Disable IRQs after channel suspend

gpu: nvgpu: Disable IRQs after channel suspend

Interrupts may be needed before we have actually silenced all
channels. Few possible scenarios include channel recovery during
teardown and sw method before the channels have been suspended.
This patch modifies the teardown path so that we disable interrupts
after the channels have been suspended.

Change-Id: Ifc36dbb74b1d36bd88d1220fa50a53c4072df4d8
Signed-off-by: Arto Merilainen <amerilainen@nvidia.com>
Reviewed-on: http://git-master/r/394599
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>
Tested-by: Terje Bergstrom <tbergstrom@nvidia.com>