tegra: Enable CONFIG_BOOTP_PREFER_SERVERIP for all Jetson boards

This allows the user to set $serverip in the environment before
executing a DHCP request. If they do, U-Boot will use that IP rather
than using the IP in the DHCP response.

Signed-off-by: Tom Warren <twarren@nvidia.com>
Acked-by: Stephen Warren <swarren@nvidia.com>