net: fec: make PPS channel configurable

net: fec: make PPS channel configurable

commit 566c2d83887f0570056833102adc5b88e681b0c7 upstream.

Depending on the SoC where the FEC is integrated into the PPS channel
might be routed to different timer instances. Make this configurable
from the devicetree.

When the related DT property is not present fallback to the previous
default and use channel 0.

Reviewed-by: Frank Li <Frank.Li@nxp.com>
Tested-by: Rafael Beims <rafael.beims@toradex.com>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.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>