net: gem: Preserve clk on emio interface

Avoid overwriting GEMx_RCLK_CTRL and GEMx_CLK_CTRL
if the Ethernet interface is connect on EMIO

Do not enable emio for this standard board configuration for now.

Signed-off-by: David Andrey <david.andrey@netmodule.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Tom Rini <trini@ti.com>