net: fec: do not access reserved register for i.MX8M

The MIB RAM and FIFO receive start register does not exist on
i.MX8M. Accessing these register will cause system hang.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Stefano Babic <sbabic@denx.de>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Stefano Babic <sbabic@denx.de>

drivers/net/fec_mxc.c

@@ -562,8 +562,8 @@ static int fec_init(struct eth_device *dev, bd_t *bd)
 	writel(0x00000000, &fec->eth->gaddr1);
 	writel(0x00000000, &fec->eth->gaddr2);
 
-	/* Do not access reserved register for i.MX6UL */
-	if (!is_mx6ul() && !is_mx6ull()) {
+	/* Do not access reserved register */
+	if (!is_mx6ul() && !is_mx6ull() && !is_mx8m()) {
 		/* clear MIB RAM */
 		for (i = mib_ptr; i <= mib_ptr + 0xfc; i += 4)
 			writel(0, i);