net: fman: Get PCS node in per-mac init

This moves the reading of the PCS property out of the generic probe and
into the mac-specific initialization function. This reduces the
mac-specific jobs done in the top-level probe function.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Acked-by: Camelia Groza <camelia.groza@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>