releasetools: Add radio images to fastboot packages

Fastboot packages should include radio images, if they exist. Also
generate a flash-radio.sh file if a filesmap file exists to indicate
the partition that a radio image should be flashed to.

Change-Id: Ic3392cc76407408b98aad00f36f4dfa3b9be176b
Merge remote-tracking branch 'cm/cm-11.0' into cm-11.0