drm/v3d: Use drm_gem_lock_reservations()/drm_gem_unlock_reservations()

Now that we have core helpers, this gets rid of a lot of boilerplate.

Signed-off-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20190308161716.2466-3-eric@anholt.net


Acked-by: Rob Herring <robh@kernel.org>