tpm-backend: Made few interface methods optional

This allows backend implementations left optional interface methods.
For mandatory methods assertion checks added.

Took the opportunity to remove unused methods:
 - tpm_backend_get_desc()
 - TPMDriverOps->handle_startup_error

Signed-off-by: Amarnath Valluri <amarnath.valluri@intel.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Stefan Berger<stefanb@linux.vnet.ibm.com>
Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/tpm.c b/tpm.c
index b19b1a3..db14849 100644
--- a/tpm.c
+++ b/tpm.c
@@ -62,7 +62,7 @@ static void tpm_display_backend_drivers(void)
             continue;
         }
         fprintf(stderr, "%12s   %s\n",
-                TpmType_str(i), be_drivers[i]->desc());
+                TpmType_str(i), be_drivers[i]->desc);
     }
     fprintf(stderr, "\n");
 }