drm/ttm: return ENOSPC from ttm_bo_mem_space v3

Only convert it to ENOMEM in ttm_bo_validate.

This allows ttm_bo_validate to distinguish between an out of memory
situation and just out of space in a placement domain.

v2: improve commit message
v3: fix kerneldoc typos

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Zack Rusin <zack.rusin@broadcom.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240112125158.2748-3-christian.koenig@amd.com