drm/ttm: Increase pool shrinker batch target

drm/ttm: Increase pool shrinker batch target

The default core shrink target of 128 pages (SHRINK_BATCH) is quite low
relative to how cheap TTM pool shrinking is, and how the free pages are
distributed in page order pools.

We can make the target a bit more aggressive by making it roughly the
average number of pages across all pools, freeing more of the cached
pages every time shrinker core invokes our callback.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Tvrtko Ursulin <tursulin@ursulin.net>
Link: https://lore.kernel.org/r/20250603112750.34997-3-tvrtko.ursulin@igalia.com