clk: imx: vf610: leave DDR clock on

To use STOP mode without putting DDR3 into self-refresh mode, we
need to keep the DDR clock enabled. Use the new gate configuration
with a value of 2 to make sure that the clock is enabled in RUN,
WAIT and STOP mode.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>