ARM: imx6sl: add missing enet clock for imx6sl

There's a enet clock gate missing in clock tree, thus add it.

Signed-off-by: Fugang Duan <B38611@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>

diff --cc arch/arm/mach-imx/clk-imx6sl.c
Simple merge

diff --cc include/dt-bindings/clock/imx6sl-clock.h
Simple merge