Add CONFIG_LOCALVERSION_AUTO_GIT_TAG_GLOB

"git describe" prints the most recent tag it can find in the git repo.
The Makefile bakes the output into the version string. If the most
recent tag turns out to be a SpaceCast tag, I get version strings that
cointain something like "spacecast-3.8-6-gafe9d1f" even if I build for
GFiber devices.

Add CONFIG_LOCALVERSION_AUTO_GIT_TAG_GLOB which allows us to pass a
"--match" option to git describe. If we set it to "gfiber*", we'll only
get gfiber tags.

Change-Id: Ic751cef172f51b997d1f10aafd22477d027a87c9
3 files changed