drm/amdgpu/gfx9: fullfill kiq irq funcs (v2)

Fullfill KIQ irq funcs to support kiq interrupt.

v2: squash in adding interrupt src

Signed-off-by: Xiangliang Yu <Xiangliang.Yu@amd.com>
Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>