x86, gart: Don't enforce GART aperture lower-bound by alignment

x86, gart: Don't enforce GART aperture lower-bound by alignment

This patch changes the allocation of the GART aperture to
enforce only natural alignment instead of aligning it on
512MB. This big alignment was used to force the GART
aperture to be over 512MB. This is enforced by using 512MB
as the lower-bound address in the allocation range.

[ hpa: The actual number 512 MiB needs to be revisited, too. ]

Cc: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Link: http://lkml.kernel.org/r/1303134346-5805-2-git-send-email-joerg.roedel@amd.com
Signed-off-by: H. Peter Anvin <hpa@zytor.com>