Re-worked devicetree.cb for DL145 G1

Re-worked devicetree.cb for DL145 G1

After a lot of experimentation this commit improves some hardware
features that were not recognized or incorrectly configured before.
The only thing not tested is SCSI-option board (I dont have one).
Misleading errors in comments have been corrected.
(Note BTW that the DL145 G1 mainboard is identical to AMD Serenade
which was supported in early versions of coreboot but was dropped
for some reason.)

Signed-off-by: Oskar Enoksson <enok@lysator.liu.se>
Change-Id: Ibbd97fafad22196b1e18d0b257731490339f113e
Reviewed-on: http://review.coreboot.org/237
Tested-by: build bot (Jenkins)
Reviewed-by: Marc Jones <marcj303@gmail.com>