drm/xe/bo: Evict VRAM to TT rather than to system

drm/xe/bo: Evict VRAM to TT rather than to system

The main difference is that we don't bounce and sync on eviction, allowing
for pipelined eviction. Moving forward we also need to be careful with
dma mappings which can be released in SYSTEM but may remain in TT.

v2:
- Remove a stale comment (Matthew Brost)

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230626181741.32820-5-thomas.hellstrom@linux.intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>