agp/uninorth: Fix oops caused by flushing too much

This fixes a sporadic oops at boot on G5 Power Macs.  The table_end
variable has the address of the last byte of the table.  Adding on
PAGE_SIZE means we flush too much, and if the page after the table
is not mapped for any reason, the kernel will oops.  Instead we add
on 1 because flush_dcache_range() interprets its second argument as
the first byte past the range to be flushed.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>