[PATCH] x86_64: use select for GART_IOMMU to enable AGP

The AGP default doesn't work well with other selects, so use a select for
GART_IOMMU as well.  Remove a redundant default for SWIOTLB as well.

Signed-off-by: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Andi Kleen <ak@muc.de>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Dave Airlie <airlied@linux.ie>
Cc: Jeff Garzik <jeff@garzik.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>