vgabios: Make cirrus line lengths standard.

Only two modes don't match their expected line length.  One looks like
a bug (it has a virtual line length of 1280 for a screen of 1600
bytes) and one looks like an optimization (2048 vs 1920).  Change the
mode line lengths to exactly match the expected line lengths so that
the VBE code is correct.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>