drm/i915: Always write both TILEOFF and LINOFF plane registers

Reduce the clutter in the sprite update functions by writing
both TILEOFF and LINOFF registers unconditionally. We already
did this for primary planes so might as well do it for the
sprites too.

There is no harm in writing both registers. Which one gets
used depends on the tilimg mode selected in the plane control
registers.

It might even make sense to clear the register that won't
get used. That could make register dumps a little easier to
parse. But I'm not sure it's worth the extra hassle.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181108150955.23948-1-ville.syrjala@linux.intel.com
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> #irc