bmaptool: put the PV in the filename

bmaptool: put the PV in the filename

We're shipping a release but the filename suggests it is a git snapshot.

To avoid version-going-backwards errors we need to continue to put +git
in the PV, so add a comment to remind the upgrader to remove it.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>