block: Rename raw_bsd to raw-format.c

Given that we have raw-win32.c and raw-posix.c, my initial guess at
raw_bsd.c was that it was for dealing with raw files using code
specific to the BSD operating system (beyond what raw-posix could
do).  Not so - this name was chosen back in commit e1c66c6 to
distinguish that it was a BSD licensed file, in contrast to the
then-existing raw.c with an unclear and potentially unusable
license.  But since it has been more than three years since the
rewrite, it's time to pick a more useful name for this file to
avoid this type of confusion to future contributors that don't know
the backstory, as none of our other files are named solely by the
license they use.

In reality, this file deals with the raw format, which is useful
with any number of protocols, while raw-{win32,posix} deal with
the file protocol (and in turn, that protocol is not limited to
use with the raw format).  So rename raw_bsd to raw-format.c.  We
could have also used the shorter name raw.c, except that collides
with the earlier use of that filename for a different license,
and it's better to be safe than risk license pollution.

The next patch will also rename raw-win32.c and raw-posix.c to
further distinguish the difference in roles.

It doesn't hurt that this gets rid of an underscore in the filename,
thereby making tab-completion on 'ra<TAB>' easier (now I don't have
to type the shift key, which slows things down :)

Suggested-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
