i965/gen8+: Fix the number of dwords programmed in MI_FLUSH_DW

Number of dwords in MI_FLUSH_DW changed from 4 to 5 in gen8+.

Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
Cc: <mesa-stable@lists.freedesktop.org>
(cherry picked from commit 1dc45d75)
[Andres Gomez: brw->gen not yet dropped in favor of devinfo->gen]
Signed-off-by: Andres Gomez <agomez@igalia.com>

Conflicts:
	src/mesa/drivers/dri/i965/brw_pipe_control.c
	src/mesa/drivers/dri/i965/intel_blit.c