net: replace the "xfi" phy-mode with "10gbase-r"

As part of the effort of making U-Boot work with the same device tree as
Linux, there is an issue with the "xfi" phy-mode. To be precise, in
Linux there was a discussion (for those who have time to read:
https://lore.kernel.org/netdev/1576768881-24971-2-git-send-email-madalin.bucur@oss.nxp.com/)

which led to a patch:
https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=c114574ebfdf42f826776f717c8056a00fa94881

TL;DR: "xfi" was standardized in Linux as "10gbase-r".

This patch changes the relevant occurrences in U-Boot to use "10gbase-r"
instead of "xfi" wherever applicable.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
diff --git a/board/freescale/ls1088a/README b/board/freescale/ls1088a/README
index aa0fb6a..5315909 100644
--- a/board/freescale/ls1088a/README
+++ b/board/freescale/ls1088a/README
@@ -42,7 +42,7 @@
  - SERDES Connections, 16 lanes supporting:
       - PCI Express - 3.0
       - SATA 3.0
-      - XFI
+      - 10GBase-R
       - QSGMII
  - DDR Controller
      - One ports of 72-bits (8-bits ECC, 64-bits DATA) DDR4. Each port supports four
@@ -106,7 +106,7 @@
  - SERDES Connections, 16 lanes supporting:
       - PCI Express - 3.0
       - SATA 3.0
-      - 2 XFI
+      - 2 10GBase-R
       - QSGMII, SGMII with help for Riser card
       - 2 RGMII
       - 5 slot for Riser card or PCIe NIC