[AGP] size AGP mem correctly when memory is discontiguous.

This removes the agpgart assumption that memory is contiguous.

drivers/char/agp/backend.c

@@ -86,7 +86,7 @@ static int agp_find_max (void)
 {
 	long memory, index, result;
 
-	memory = virt_to_phys(high_memory) >> 20;
+	memory = (num_physpages << PAGE_SHIFT) >> 20;
 	index = 1;
 
 	while ((memory > maxes_table[index].mem) && (index < 8))