releasetools: Add support for BML partition type

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

Change-Id: I59f9da9c4832f791f2e126257d2ed777d6104ad8
Kernel makefiles that the stat on the system is GNU stat. GNU stat uses the "-c" option to specify format.
Darwin stat uses the "-f" option to specify format. This discrepency will cause kernel build breaks.
On my system, I symlink stat to GNU stat. This causes the "get-file-size" define
to fail.
The fix for this is to detect "gstat", aka GNU stat, and use that appropriately.

Change-Id: I987c155b7dc3ff14ffe6da40edf834ca34b7df75