drm/amdkfd: Make KFD support on Hawaii experimental

Hawaii support is mostly untested these days. ROCm user mode also
depends on custom firmware for AQL packet processing, that was never
pushed upstream due to quality regressions in graphics driver testing.

Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Kent Russell <kent.russell@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>