drm/ttm: Avoid invoking the OOM killer when reading back swapped content

drm/ttm: Avoid invoking the OOM killer when reading back swapped content

In situations where the system is very short on RAM, the shmem
readback from swap-space may invoke the OOM killer.

However, since this might be a recoverable situation where the caller
is indicating this by setting
struct ttm_operation_ctx::gfp_retry_mayfail to true, adjust the gfp
value used by the allocation accordingly.

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Maarten Lankhorst <dev@lankhorst.se>
Acked-by: Christian König <christian.koening@amd.com>
Link: https://patch.msgid.link/20260317141856.237876-3-thomas.hellstrom@linux.intel.com