Rename "system-options" to "systemd-efi-options"

This makes the naming more consistent: we now have
bootctl systemd-efi-options,
$SYSTEMD_EFI_OPTIONS
and the SystemdOptions EFI variable.

(SystemdEFIOptions would be redundant, because it is only used in the context
of efivars, and users don't interact with that name directly.)

bootctl is adjusted to use 2sp indentation, similarly to systemctl and other
programs.

Remove the prefix with the old name from 'bootctl systemd-efi-options' output,
since it's redundant and we don't want the old name anyway.

src/basic/proc-cmdline.c

@@ -119,7 +119,7 @@ int proc_cmdline_parse(proc_cmdline_parse_t parse_item, void *data, ProcCmdlineF
 
         /* We parse the EFI variable first, because later settings have higher priority. */
 
-        r = efi_systemd_options_variable(&line);
+        r = systemd_efi_options_variable(&line);
         if (r < 0 && r != -ENODATA)
                 log_debug_errno(r, "Failed to get SystemdOptions EFI variable, ignoring: %m");
 
@@ -250,7 +250,7 @@ int proc_cmdline_get_key(const char *key, ProcCmdlineFlags flags, char **ret_val
                 return r;
 
         line = mfree(line);
-        r = efi_systemd_options_variable(&line);
+        r = systemd_efi_options_variable(&line);
         if (r == -ENODATA)
                 return false; /* Not found */
         if (r < 0)