drm/amdgpu - Disable all irqs before disabling all CRTCs

By moving amdgpu_irq_disable_all earlier in the sequence
fixes an issue with disabling pflip interrupts:

*ERROR* dal_irq_service_dummy_ack: called for non-implemented irq source

Earlier patch fixed a memory corruption and revealed irq
warnings.This way it seems to be there no obvious issues
with unloading the module.

Signed-off-by: Mikita Lipski <mikita.lipski@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>