net: fec: refactor PPS channel configuration

net: fec: refactor PPS channel configuration

commit bf8ca67e21671e7a56e31da45360480b28f185f1 upstream.

Preparation patch to allow for PPS channel configuration, no functional
change intended.

Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Csókás, Bence <csokas.bence@prolan.hu>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Csókás, Bence <csokas.bence@prolan.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>