drm/radeon/kms: fix a regression on r7xx AGP due to the HDP flush fix

commit: 812d046915f48236657f02c06d7dc47140e9ceda
drm/radeon/kms/r7xx: add workaround for hw issue with HDP flush
breaks on AGP boards since there is no VRAM gart table.

This patch fixes the issue by creating a VRAM scratch page so that
can be used on both AGP and PCIE.

Fixes:
https://bugs.freedesktop.org/show_bug.cgi?id=29834

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/radeon/r600.c b/drivers/gpu/drm/radeon/r600.c
index d0ebae9..aee8376 100644
--- a/drivers/gpu/drm/radeon/r600.c
+++ b/drivers/gpu/drm/radeon/r600.c
@@ -3541,7 +3541,7 @@
 	 * rather than write to HDP_REG_COHERENCY_FLUSH_CNTL
 	 */
 	if ((rdev->family >= CHIP_RV770) && (rdev->family <= CHIP_RV740)) {
-		void __iomem *ptr = (void *)rdev->gart.table.vram.ptr;
+		void __iomem *ptr = (void *)rdev->vram_scratch.ptr;
 		u32 tmp;
 
 		WREG32(HDP_DEBUG1, 0);