drm/xe: Force write completion of MI_STORE_DATA_IMM

With Force write completion unset there is no guarantees of when the
write will be globally visible what is not the behavior wanted.

Fixes: 9c57bc08 ("drm/xe/lnl: Drop force_probe requirement")
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241217160732.46280-1-jose.souza@intel.com