build: Support nam configuration script in ota package

Similar to the --backup command that allows adding the backup and
restore script, this allows the use of --configid to append the
modelid_cfg script below the backuptool, as previously configured in
CM7 builds.
This adds support for devices that originate from other countries, but
have a North American counterpart that requires alternate GPS and sound
profiles.
Unlike backup tool, which uses the cm prefix to an existing lunch combo
variable, this flag can apply to devices not currently supported by CM.
The supported devices are manufactured by HTC, so instead of verifying
a cm prefix, the htc_ component is used to trigger the append.