viafb: vt1636 cleanup

This patch merges tbl1636 into vt1636 and cleans it up as the data was
only used there anyway. No runtime changes are expected.

Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Cc: Joseph Chan <JosephChan@via.com.tw>