i965: Program DWord Length in MI_FLUSH_DW

Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
Cc: <mesa-stable@lists.freedesktop.org>
(cherry picked from commit 6165fda5)

Squashed with:

i965: Remove DWord length from MI_FLUSH_DW definition

Fixes: 6165fda5 ("i965: Program DWord Length in MI_FLUSH_DW")
Cc: <mesa-stable@lists.freedesktop.org>
Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Nanley Chery <nanley.g.chery@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
(cherry picked from commit 822fd234)