When trap_ctrl.trap_after_inst is set, it is possible for a wave to
enter the trap handler, after single-stepping an instruction and a
save_context is raised, with only save_context set in excp_flag_priv.

Because excp_flag_priv.trap_after_inst is not reliably set, we need to
use the missed single-step workaround for gfx12 as well.

Also add wave_start and wave_end as exceptions that should be handled
by the 2nd level trap handler.
Signed-off-by: Laurent Morichetti <laurent.morichetti@amd.com>
Tested-by: Lancelot Six <lancelot.six@amd.com>
Reviewed-by: Jonathan Kim <jonathan.kim@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>