drm/radeon/kms/r7xx: add regs for 40 bit CUR/GRPH addresses

The *_HIGH regs are reversed. The secondary ones are in the
primary block and vice versa.

We currently only use a 32 bit internal address, so these are
0 for now.

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>