drm/ttm: improve idle/busy handling v5

Previously we would never try to move a BO into the preferred placements
when it ever landed in a busy placement since those were considered
compatible.

Rework the whole handling and finally unify the idle and busy handling.
ttm_bo_validate() is now responsible to try idle placement first and then
use the busy placement if that didn't worked.

Drawback is that we now always try the idle placement first for each
validation which might cause some additional CPU overhead on overcommit.

v2: fix kerneldoc warning and coding style
v3: take care of XE as well
v4: keep the ttm_bo_mem_space functionality as it is for now, only add
    new handling for ttm_bo_validate as suggested by Thomas
v5: fix bug pointed out by Matthew

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Zack Rusin <zack.rusin@broadcom.com> v3
Link: https://patchwork.freedesktop.org/patch/msgid/20240229134003.3688-1-christian.koenig@amd.com
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>