mesa: add -mesa suffix to GL packages, RPROVIDE their generic names

mesa: add -mesa suffix to GL packages, RPROVIDE their generic names

When Debian-renaming, all packages that provide GL libraries get renamed to the
same name, and it's entirley possible for a feed to have multiple GL libraries
in.  This obviously creates conflicts.

Resolve this for Mesa by forcing the package names to be of the form libgl-mesa,
and RPROVIDE libgl.

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>