rockchip: defconfig: puma-rk3399: enable OF_LIVE (live tree)

With the critical drivers ready for switching to a live tree, we can
now enable it in the defconfig for the RK3399-Q7.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Simon Glass <sjg@chromium.org>