init: Add support for gzipped firmware files

In case no matching firmware is found, re-search the paths for
[path][firmware].gz and use that instead if found.

Reviewed-on: http://gerrit.mot.com/724787


SLTApproved: Slta Waiver <sltawvr@motorola.com>
Tested-by: Jira Key <jirakey@motorola.com>
Reviewed-by: Wen-Long Che <wenlong@motorola.com>
SME-Granted: Gerrit Application <gerritmailarchive@motorola.com>
Reviewed-by: Christopher Fries <cfries@motorola.com>
Submit-Approved: Jira Key <jirakey@motorola.com>

Adapted for Marshmallow by Benjamin Legrand (scritch007)

Change-Id: I74e42ab3c77eb7722c58042489d7bd4856f3be63