scripts: fix generation update-binfmts templates

This patch fixes the update-binfmts templates being used in the script
scripts/qemu-binfmt-conf.sh when the option --debian is used.

Fixed issues are:
- Typo in flag 'credentials' (previously 'credential').
- Missing flags 'preserve' and 'fix_binary'.

Reference: https://manpages.debian.org/buster/binfmt-support/update-binfmts.8.en.html#FORMAT_FILES

Signed-off-by: Silvano Cirujano Cuesta <silvano.cirujano-cuesta@siemens.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20210323123457.23747-1-silvano.cirujano-cuesta@siemens.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

scripts/qemu-binfmt-conf.sh

@@ -294,7 +294,9 @@ package qemu-$cpu
 interpreter $qemu
 magic $magic
 mask $mask
-credential $CREDENTIAL
+credentials $CREDENTIAL
+preserve $PRESERVE_ARG0
+fix_binary $PERSISTENT
 EOF
 }