net: ravb: Move delay mode set in the driver's ndo_open API

Delay parsing and setting were done in the driver's probe API. As some IP
variants switch to reset mode (and thus the register contents is lost) when
setting clocks (due to module standby functionality) to be able to
implement runtime PM keep the delay parsing in the driver's probe function
and move the delay applying function to the driver's ndo_open API.

Along with it, ravb_parse_delay_mode() function was moved close to
ravb_set_delay_mode() function to have the delay specific code in the
same place.

Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>