drm/amdkfd: refine the poison data consumption handling

drm/amdkfd: refine the poison data consumption handling

The user applications maybe register the KFD_EVENT_TYPE_HW_EXCEPTION and
KFD_EVENT_TYPE_MEMORY events, driver could notify them when poison data
consumed. Beside that, some applications maybe register SIGBUS signal
hander. These applications will handle poison data by themselves, exit
or re-create context to re-dispatch works.

Signed-off-by: Dennis Li <Dennis.Li@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>