tree-wide: relax TPM available checks for many cases

In many cases it's essential to know if the firmware supports a TPM, but
in others we should accept it if the firmware doesn't have TPM support,
in particular if we want to run the OS with a software TPM.

Hence, add tpm2_is_mostly_supported() as function similar to
tpm2_is_fully_supported(), with the only difference that the former
doesn't insist on a firmware supported TPM. Then, change a number of
users over to this (but not all).

src/shared/creds-util.c

@@ -894,7 +894,7 @@ int encrypt_credential_and_warn(
                  * container tpm2_support will detect this, and will return a different flag combination of
                  * TPM2_SUPPORT_FULL, effectively skipping the use of TPM2 when inside one. */
 
-                try_tpm2 = tpm2_is_fully_supported();
+                try_tpm2 = tpm2_is_mostly_supported();
                 if (!try_tpm2)
                         log_debug("System lacks TPM2 support or running in a container, not attempting to use TPM2.");
         } else