net: sh_eth: Fix RX packets errors on R8A7740

This patch will fix RX packets errors when receiving big size
of data by set bit RNC = 1.

RNC - Receive Enable Control

0: Upon completion of reception of one frame, the E-DMAC writes
the receive status to the descriptor and clears the RR bit in
EDRRR to 0.

1: Upon completion of reception of one frame, the E-DMAC writes
(writes back) the receive status to the descriptor. In addition,
the E-DMAC reads the next descriptor and prepares for reception
of the next frame.

In addition, for get more stable when receiving packets, I set
maximum size for the transmit/receive FIFO and inserts padding
in receive data.

Signed-off-by: Nguyen Hong Ky <nh-ky@jinso.co.jp>
Signed-off-by: David S. Miller <davem@davemloft.net>