Rename unused RAM_DIAG_BG_ETH to make clear that BG RAM is not used and has MM address 0.

boards/uniboard2c/designs/unb2c_test/unb2c_test.fpga.yaml

@@ -80,7 +80,7 @@ peripherals:
       - { name: g_buf_addr_w, value: 8 }
     mm_port_names:
       - REG_DIAG_BG_ETH_0
-      - RAM_DIAG_BG_ETH_0  # not used in eth_tester_tx
+      - RAM_DIAG_BG_ETH_0_NOT_USED  # not used in eth_tester_tx
 
   - peripheral_name: eth_tester_offload_hdr_dat
     peripheral_group: eth0_tx
@@ -139,7 +139,7 @@ peripherals:
       - { name: g_buf_addr_w, value: 8 }
     mm_port_names:
       - REG_DIAG_BG_ETH_1
-      - RAM_DIAG_BG_ETH_1  # not used in eth_tester_tx
+      - RAM_DIAG_BG_ETH_1_NOT_USED  # not used in eth_tester_tx
 
   - peripheral_name: eth_tester_offload_hdr_dat
     peripheral_group: eth1_tx