fix(build): pass the PLAT option during FIP tool compilation

Due to change [1], the FIP tool was compiled with the default platform
instead of the one specified via the command line, as make_helpers.mk
set the PLAT option to default. This happened because the root Makefile
invoked FIP tool compilation without the PLAT option. The issue has
been fixed by explicitly providing the PLAT option for FIP tool
compilation.

[1]: https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/26597

Change-Id: Icc516f8d44706df03c7e6ee123b58afeda72cea7
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
diff --git a/Makefile b/Makefile
index 280f096..179e07a 100644
--- a/Makefile
+++ b/Makefile
@@ -1716,7 +1716,7 @@
 
 ${FIPTOOL}: FORCE
 ifdef UNIX_MK
-	$(q)${MAKE} CPPFLAGS="-DVERSION='\"${VERSION_STRING}\"'" FIPTOOL=${FIPTOOL} OPENSSL_DIR=${OPENSSL_DIR} DEBUG=${DEBUG} --no-print-directory -C ${FIPTOOLPATH} all
+	$(q)${MAKE} PLAT=${PLAT} CPPFLAGS="-DVERSION='\"${VERSION_STRING}\"'" FIPTOOL=${FIPTOOL} OPENSSL_DIR=${OPENSSL_DIR} DEBUG=${DEBUG} --no-print-directory -C ${FIPTOOLPATH} all
 else
 # Clear the MAKEFLAGS as we do not want
 # to pass the gnumake flags to nmake.