i945: Replace video gfx init.

Old init was a replay not even meant to have been committed.
This one really computes values and does its job. Tested on
Macbook2,1 (1280x800) and X60 (1024x768).

Change-Id: I61b6946c095fe06e20ae9a0db54696d0568225dd
Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
Reviewed-on: http://review.coreboot.org/5320
Reviewed-by: Francis Rowe <info@gluglug.org.uk>
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>