arm-bsp/scp-firmware: add comment to explain where a UUID is defined

The N1SDP build uses a non-standard FIP UUID, so explain where it comes
from.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>

meta-arm-bsp/recipes-bsp/scp-firmware/scp-firmware-n1sdp.inc

@@ -15,6 +15,7 @@ do_install:append() {
        --soc-fw "${RECIPE_SYSROOT}/firmware/bl31.bin" \
        "scp_fw.bin"
 
+   # This UUID is FIP_UUID_MCP_BL2 in SCP-Firmware.
    fiptool \
        create \
        --blob uuid=54464222-a4cf-4bf8-b1b6-cee7dade539e,file="${D}/firmware/mcp_ramfw.bin" \