drm/radeon: add a reset work handler

New asics support non-privileged IBs.  This allows us
to skip IB checking in the driver since the hardware
will check the command buffers for us.  When using
non-privileged IBs, if the CP encounters an illegal
register in the command stream, it will halt and generate
an interrupt.  The CP needs to be reset to continue.  For now
just do a full GPU reset when this happens.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>