releasetools: Add support for BML partition type

Needed for Samsung devices using proprietary FSR drivers.
Backported from gingerbread branch.

Change-Id: I59f9da9c4832f791f2e126257d2ed777d6104ad8
Merge branch 'jb-mr1' of git://github.com/Root-Box/android_build into rb-jb-mr1