net: fsl_enetc: Introduce enetc_dev_id()

Introduce mapping function enetc_dev_id(), which converts PCIe BDF of
the ENETC into linear incrementing index usable e.g. as interface index.
This replaces the current ad-hoc calculation used in the code with a
dedicated function. No functional change.

Signed-off-by: Marek Vasut <marex@denx.de>
diff --git a/drivers/net/fsl_enetc.c b/drivers/net/fsl_enetc.c
index 6398535..e6f5ca6 100644
--- a/drivers/net/fsl_enetc.c
+++ b/drivers/net/fsl_enetc.c
@@ -32,6 +32,14 @@
 	       pplat->vendor == PCI_VENDOR_ID_FREESCALE;
 }
 
+static int enetc_dev_id(struct udevice *dev)
+{
+	if (enetc_is_ls1028a(dev))
+		return PCI_FUNC(pci_get_devfn(dev));
+
+	return 0;
+}
+
 /*
  * sets the MAC address in IERB registers, this setting is persistent and
  * carried over to Linux.
@@ -109,7 +117,7 @@
 	 * PCI function # and enetc#N based on interface count
 	 */
 	if (ofnode_valid(dev_ofnode(dev)))
-		sprintf(name, "enetc-%u", PCI_FUNC(pci_get_devfn(dev)));
+		sprintf(name, "enetc-%u", enetc_dev_id(dev));
 	else
 		sprintf(name, "enetc#%u", eth_num_devices++);
 	device_set_name(dev, name);