ENGR00172274-01 - [MX6]: rework IEEE-1588 ts_clk in MX6Q ARIK CPU board.

ENGR00172274-01 - [MX6]: rework IEEE-1588 ts_clk in MX6Q ARIK CPU board.

- Fix GPIO_16 IOMUX config.
- Config GPIO_16 pad to ENET_ANATOP_ETHERNET_REF_OUT.
- IEEE-1588 ts_clk, S/PDIF in and i2c3 are mutually exclusive,
  because all of them use GPIO_16, so it only for one function
  work at a moment.
- Test result:
   	Enet work fine at 100/1000Mbps in TO1.1.
	IEEE 1588 timestamp is convergent.

Signed-off-by: Fugang Duan <B38611@freescale.com>