fix(sptool): add leading zeroes in UUID conversion

The UUID conversion drops leading zeroes, so make sure that
all hex strings always are 8 digits long

Signed-off-by: Anders Dellien <anders.dellien@arm.com>
Change-Id: I5d7e3cf3b53403a02bf551f35f17dbdb96dec8ae
diff --git a/tools/sptool/sp_mk_generator.py b/tools/sptool/sp_mk_generator.py
index f983ff3..6b1f204 100755
--- a/tools/sptool/sp_mk_generator.py
+++ b/tools/sptool/sp_mk_generator.py
@@ -1,5 +1,5 @@
 #!/usr/bin/python3
-# Copyright (c) 2020-2021, Arm Limited. All rights reserved.
+# Copyright (c) 2020-2022, Arm Limited. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 
@@ -134,7 +134,7 @@
         int.from_bytes(y[1], byteorder='little', signed=False),
         int.from_bytes(y[2], byteorder='little', signed=False),
         int.from_bytes(y[3], byteorder='little', signed=False))
-        uuid_std = uuid.UUID(f'{z[0]:04x}{z[1]:04x}{z[2]:04x}{z[3]:04x}')
+        uuid_std = uuid.UUID(f'{z[0]:08x}{z[1]:08x}{z[2]:08x}{z[3]:08x}')
 
         """
         Append FIP_ARGS