ARM: imx: enable emi_slow_gate clock for imx5

ARM: imx: enable emi_slow_gate clock for imx5

The imx5 common clock migration causes a regression with smsc911x
driver on imx53-ard board, where a smsc lan9220 controller gets
connected on imx53 with EIM interface.  EIM needs clock emi_slow_gate
to be functional.  In the new imx5 clock driver, there is no use count
incremented for the clock by enabling it, so the framework closes the
clock at late init time and makes EIM stop working then.

Enable emi_slow_gate in clock driver initialization to fix the
regression.

Cc: stable@vger.kernel.org
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>