clk: imx: vf610: Disable automatic clock gating for lpuart in LPSTOP mode

In order to allow wake support in STOP sleep mode, clocks are needed. Use
imx_clk_gate2_cgr to disable automatic clock gating in low power mode STOP.
This allows to enable wake by UART using:
echo enabled > /sys/class/tty/ttyLP0/power/wakeup

However, if wake is not enabled, the driver should disable the clocks explicitly
to save power.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Bhuvanchandra DV <bhuvanchandra.dv@toradex.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/20160628053235.5114-3-bhuvanchandra.dv@toradex.com