net: mvpp2: increase PHY reset pulse

The default Linux PHY reset delay is 10ms. This is also the requirement
for Marvell 88E151x PHYs, which are likely to be used with this Ethernet
MAC.

Cc: Stefan Chulski <stefanc@marvell.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Stefan Roese <sr@denx.de>