Revert "drm/ttm: increase ttm pre-fault value to PMD size"

This reverts commit 0ddd2ae5.

This patch causes sluggishness and stuttering in graphical
apps.

Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3564
Link: https://www.spinics.net/lists/dri-devel/msg457005.htmlSigned-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: Zhu Lingshan <lingshan.zhu@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240820134600.1909370-1-alexander.deucher@amd.com

include/drm/ttm/ttm_bo.h

@@ -39,11 +39,7 @@
 #include "ttm_device.h"
 
 /* Default number of pre-faulted pages in the TTM fault handler */
-#if CONFIG_PGTABLE_LEVELS > 2
-#define TTM_BO_VM_NUM_PREFAULT (1 << (PMD_SHIFT - PAGE_SHIFT))
-#else
 #define TTM_BO_VM_NUM_PREFAULT 16
-#endif
 
 struct iosys_map;