drm/amdgpu: Fix module unload hang by KIQ IRQ set

In some cases, manually insmod/rmmod amdgpu is necessary. When
unloading amdgpu, the KIQ IRQ enable/disable function will case
system hang. The root cause is, in the sequence of function
amdgpu_fini, the sw_fini of IP block AMD_IP_BLOCK_TYPE_GFX will be
invoked earlier than that of AMD_IP_BLOCK_TYPE_IH. So continue to use
the variable freed by AMD_IP_BLOCK_TYPE_GFX will cause system hang.

Signed-off-by: Trigger Huang <trigger.huang@amd.com>
Reviewed-by: Xiangliang Yu &lt; <Xiangliang.Yu@amd.com>
Reviewed-by: Monk Liu <monk.liu@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>