drm/amdkfd: add debug set exceptions enabled operation

The debugger subscibes to nofication for requested exceptions on attach.
Allow the debugger to change its subsciption later on.

Signed-off-by: Jonathan Kim <jonathan.kim@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>