MLK-16118-6 net: fec_mxc: Add the init_clk_fec function for non-DM driver

MLK-16118-6 net: fec_mxc: Add the init_clk_fec function for non-DM driver

When the power domain driver is enabled, we need to enable clocks after power
domain on. So the clock settings can't set in board_init, needs to set them
when the device is probed. Add this weak function in driver, that SoC codes
can implement the clock settings.

Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Ye Li <ye.li@nxp.com>
(cherry picked from commit c0e4ac66196b20f363f711fb18e40b70e3be9240)
(cherry picked from commit 187ea376980be12e69c45bd6e62c7ca1559046f6)