code_relocation: use named fields in string templates

Previously the script used templates where the fields were identified by
numeric ordinal-identified placeholders. This makes the code hard to read
because it is hard to tell which string corresponds to which placeholder
in the substitution.

This patch corrects the issue by replacing the ordinal placeholders with
named placeholders.

Signed-off-by: Joel Holdsworth <jholdsworth@nvidia.com>