battery-gb.c: add new functions from Greybus spec document.

Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>
greybus_manifest.h: add FIXME for version

The version field is going to go away, but after the demo, not before.
Note that in the header file.

Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>