net: dwc: add a common empty ops eqos_null_ops

Add a common empty ops: eqos_null_ops() to remove the duplicated empty
functions and reduce the driver size for stm32 and imx config.

This patch also aligns the prototype of ops 'eqos_stop_clks' with other
eqos ops by adding return value.

Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
1 file changed