[PARISC] Fix GSC graphics cards with 64MB regions

Make knapps work with its 64MB gfx card.  I probably just broke another
machine in the process, but assuming 64MB when 64MB aligned is probably
safer than assuming 32MB all the time.

Signed-off-by: Matthew Wilcox <willy@parisc-linux.org>
Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>