The 1.5 version of Engicam's i.Core MX6 CPU module features a different clock
provider for the ethernet's PHY interface. Adjust the FEC ptp clock to
reference CLK_ENET_REF clock source, and set SION bit of
MX6QDL_PAD_GPIO_16__ENET_REF_CLK to adjust the input path of that pin.

The newly introduced imx6ql-icore-1.5.dtsi allows to collect in a single
place differences between version '1.0' and '1.5' of the module.
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>