IAR: Restore support for projects not enabling policy CMP0057

Since commit 5b9bfe738c (IAR: Moved search logic to BinUtils.,
2021-07-19, v3.21.1~14^2), we use the `IN_LIST` operator in the
`CMakeFindBinUtils` module.  Set policy `CMP0057` to ensure it is
available regardless of the project's policy settings.

Fixes: #22640