bootdevice: Add interface to gather LCHS

bootdevice: Add interface to gather LCHS

Add an interface to provide direct logical CHS values for boot devices.
We will use this interface in the next commits.

Reviewed-by: Karl Heubaum <karl.heubaum@oracle.com>
Reviewed-by: Arbel Moshe <arbel.moshe@oracle.com>
Signed-off-by: Sam Eiderman <shmuel.eiderman@oracle.com>
Signed-off-by: Sam Eiderman <sameid@google.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>