tpm2: downgrade most log functions from error to debug

Because most TPM2 functions here are 'library-like' functions, they should be
at debug level, not error level.

The only functions not reduced to logging at debug are tpm2_list_devices(),
since it is expected to print output, and the tpm2_parse_pcr_argument_*()
functions, since the system-wide parse_*_argument() functions generally log at
error level.

src/tpm2-setup/tpm2-setup.c

@@ -198,7 +198,7 @@ static int load_public_key_tpm2(struct public_key_data *ret) {
 
         r = tpm2_context_new(arg_tpm2_device, &c);
         if (r < 0)
-                return r;
+                return log_error_errno(r, "Failed to create TPM2 context: %m");
 
         r = tpm2_get_or_create_srk(
                         c,
@@ -208,7 +208,7 @@ static int load_public_key_tpm2(struct public_key_data *ret) {
                         /* ret_qname= */ NULL,
                         NULL);
         if (r < 0)
-                return r;
+                return log_error_errno(r, "Failed to get or create SRK: %m");
         if (r > 0)
                 log_info("New SRK generated and stored in the TPM.");
         else