drm/radeon/kms: Convert RS690/RS740 to new init path (V2).

Also cleanup register specific to RS690/RS740. Version 2 add
missing header file for register, remove unecessary call to AGP
function and fix an indentation bug.

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