docs: def get_supported_boot_mode(self):
          """Retrieves the supported boot mode.
  
          :returns: any one of the following proliantutils.ilo.constants:
  
              SUPPORTED_BOOT_MODE_LEGACY_BIOS_ONLY,
              SUPPORTED_BOOT_MODE_UEFI_ONLY,
              SUPPORTED_BOOT_MODE_LEGACY_BIOS_AND_UEFI
  
          """
          data = self._execute_command(
              'GET_SUPPORTED_BOOT_MODE', 'SERVER_INFO', 'read')
          supported_boot_mode = (
              data['GET_SUPPORTED_BOOT_MODE']['SUPPORTED_BOOT_MODE']['VALUE'])
          return mappings.GET_SUPPORTED_BOOT_MODE_RIBCL_MAP.get(
              supported_boot_mode)