net: fec: add post PHY reset delay DT property

Some PHY require to wait for a bit after the reset GPIO has been
toggled. This adds support for the DT property `phy-reset-post-delay`
which gives the delay in milliseconds to wait after reset.

If the DT property is not given, no delay is observed. Post reset delay
greater than 1000ms are invalid.

Signed-off-by: Quentin Schulz <quentin.schulz@free-electrons.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Fugang Duan <fugang.duan@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>