Require that all headers are guarded by a symbol named

  LIBVIRT_$FILENAME

where $FILENAME is the uppercased filename, with all characters
outside a-z changed into '_'.

Note we do not use a leading __ because that is technically a
namespace reserved for the toolchain.
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

Create a virscsihost.c and place the functions there. That removes the
last #ifdef __linux__ from virutil.c.

Take the opporunity to also change the function names and in one case
the parameters slightly