arm-bsp/trusted-firmware-a: fvp-base prepend fixes

FILESEXTRAPATHS that have a prepend should have a trailing ':' to allow
for the follow-on modifications to the string.  Add it here where
necessary.

Reported-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Jon Mason <jon.mason@arm.com>

meta-arm-bsp/recipes-bsp/trusted-firmware-a/trusted-firmware-a-fvp-base.inc

@@ -4,7 +4,7 @@
 # Armv8-A Base Platform FVP
 #
 
-FILESEXTRAPATHS:prepend := "${THISDIR}/files/:${THISDIR}/files/fvp-base"
+FILESEXTRAPATHS:prepend := "${THISDIR}/files/:${THISDIR}/files/fvp-base:"
 
 SRC_URI:append = " \
     file://optee_spmc_maifest.dts;subdir=git/plat/arm/board/fvp/fdts \