drm/radeon/kms: Avoid crash when trying to cleanup uninitialized structure

Add boolean to record if some part of the driver are initialized or
not this allow to avoid a crash when trying to cleanup uninitialized
structure members.

Signed-off-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>