ARM: imx: clk-vf610: Add clock for UART4 and UART5

Add support for clock gating of UART4 and UART5.
We use these UART's in a (not yet mainlined)
device tree.

Signed-off-by: Bhuvanchandra DV <bhuvanchandra.dv@toradex.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>