drm/radeon: Change the default to PCI on PowerPC

AGP mode is unstable on PowerPC. Symptoms are generally of the form:

[ 1228.795711] radeon 0000:00:10.0: ring 0 stalled for more than 10240msec

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Mathieu Malaterre <malat@debian.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_drv.c

@@ -168,7 +168,12 @@ int radeon_no_wb;
 int radeon_modeset = -1;
 int radeon_dynclks = -1;
 int radeon_r4xx_atom = 0;
+#ifdef __powerpc__
+/* Default to PCI on PowerPC (fdo #95017) */
+int radeon_agpmode = -1;
+#else
 int radeon_agpmode = 0;
+#endif
 int radeon_vram_limit = 0;
 int radeon_gart_size = -1; /* auto */
 int radeon_benchmarking = 0;