sna: Pass MOVE_READ for partial TearFree move-to-gpu

sna: Pass MOVE_READ for partial TearFree move-to-gpu

When fixing up a pending shadow pageflip for TearFree, we must tell it
that it needs to flush the damage for a partial move-to-gpu. Even though
the current area does not read from the destination, the move-to-gpu
callback is a global pass, and we need to assume the worst for the
region outside of the target.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=72343
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>