drm/radeon/kms: fix some GART table entry bugs.

1. rv370 can accept 40-bit addresses - also at 24-bit shift not 4 bits
2. rs480 table can be in 40-bit space. - 4 bit shift for top 8 bits
3. rs480 table entries can be in 40-bit space.

Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/radeon/radeon_gart.c b/drivers/gpu/drm/radeon/radeon_gart.c
index d343a15..2977539 100644
--- a/drivers/gpu/drm/radeon/radeon_gart.c
+++ b/drivers/gpu/drm/radeon/radeon_gart.c
@@ -177,7 +177,7 @@
 			return -ENOMEM;
 		}
 		rdev->gart.pages[p] = pagelist[i];
-		page_base = (uint32_t)rdev->gart.pages_addr[p];
+		page_base = rdev->gart.pages_addr[p];
 		for (j = 0; j < (PAGE_SIZE / 4096); j++, t++) {
 			radeon_gart_set_page(rdev, t, page_base);
 			page_base += 4096;