Rework TPM measurements

Rework TPM measurements to use fewer PCRs. After discussion with upstream,
it's preferable to avoid using so many PCRs. Instead, measure into PCRs 8
and 9 but use a prefix in the event log to indicate which subsystem carried
out the measurements.

grub-core/script/execute.c

@@ -961,8 +961,8 @@ grub_script_execute_cmdline (struct grub_script_cmd *cmd)
 				   argv.args[i]);
   }
   cmdstring[cmdlen-1]= '\0';
-  grub_tpm_measure ((unsigned char *)cmdstring, cmdlen, GRUB_COMMAND_PCR,
-		    cmdstring);
+  grub_tpm_measure ((unsigned char *)cmdstring, cmdlen, GRUB_ASCII_PCR,
+		    "grub_cmd", cmdstring);
   grub_free(cmdstring);
   invert = 0;
   argc = argv.argc - 1;