Not entirely convinced 0x004018 transitions are correct yet, but, it's
an improvement.

The 750MHz value comes from fiddling with the binary driver + coolbits on
two different DDR3 NVA8 chipsets (T510 NVS3100M, and NVS300), not a clue
where this number comes from.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>