drm/amdgpu: Enable BAD_OPCODE intr for gfx8

This enables KFD_EVENT_TYPE_HW_EXCEPTION notifications to user mode in
response to bad opcodes in a CP queue.

Signed-off-by: Harish Kasiviswanathan <Harish.Kasiviswanathan@amd.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>