net: stmmac: fix num_por initialization

Driver missed initializing num_por which is one of the por values that
driver configures to hardware. In order to get these values, add a new
structure ethqos_emac_driver_data which holds por and num_por values
and populate that in driver probe.

Fixes: a7c30e62

 ("net: stmmac: Add driver for Qualcomm ethqos")
Reported-by: Rahul Ankushrao Kawadgave <rahulak@qti.qualcomm.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Reviewed-by: Amit Kucheria <amit.kucheria@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>