drm/amdgpu: more descriptive message if HMM not enabled

If using old kernel config file, CONFIG_ZONE_DEVICE is not selected,
so CONFIG_HMM and CONFIG_HMM_MIRROR is not enabled, the current driver
error message "Failed to register MMU notifier" is not clear. Inform
user with more descriptive message on how to fix the missing kernel
config option.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109808



Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>